Switching apparatus

Abstract

 Apparatus (7) for switching a filament lamp (2) in a load circuit (1) by short circuiting the load switch (3) of the load circuit (1) comprises a relay (RL1) with contacts (9) to short circuit the switch (3). The apparatus (7) switches on the load circuit (1) in response to an infra-red detector (8) detecting the presence of an intruder within the perimeter of a compound or building. A power circuit (16) comprising a rechargable battery (B1) and storage capacitor (C3) powers the relay (RL1). The power circuit (16) derives its power from the load circuit (1) across the terminals of the switch (3), when the switch (3) is open and the relay contacts (9) are open. In this condition, a battery and storage capacitor in the power circuit (16) are charged.

Description

[0001] The present invention relates to apparatus for switching a load circuit in response to an intruder or remotely transmitted signal being detected, the load circuit comprising a load fed through a switch, the apparatus being of the type comprising detecting means to detect an intruder or signal, short circuit means to short circuit the switch of the load circuit, the short circuit means being responsive to the detecting means, a power circuit to power the short circuit means and charging means to charge the power circuit.

[0002] In many cases, it is important to be able to illuminate the perimeter of a building, compound or the like. This is particularly so for security reasons. However, in general, because of the energy consumption of suitable lighting, it is usually not feasible to keep the perimeter lighting on throughout the hours of darkness. To overcome this problem, apparatus is provided which comprises a detector which can detect the presence of an intruder or an intruder about to enter the perimeter of a building, compound, or the like. Such apparatus, in general, comprises a detection circuit, usually comprising an infra-red detector which detects the infra-red radiated from the intruder. On detecting infra-red radiation, the detector activates a switch means which brings on the perimeter lighting. However, the problem with such known apparatus is that, in general, the detection circuit has to be connected into a power supply, and this normally requires that it be wired from a fuse board or other suitable power source. Furthermore, the detection circuit also has to be wired into the lighting circuit to bring on the lights. The main problem with such apparatus is that because of the complexity of the connections required to be made to the apparatus, it is generally unsuitable for installation by an average do-it-yourself enthusiast or handyman. It is essential that such known apparatus should be installed by a skilled electrician. This, it will be appreciated, has considerable disadvantages in that it requires one to obtain the services of a skilled electrician to make the necessary connections, which in many cases can be difficult, and furthermore, and more importantly, considerably increase the cost of such apparatus, since installation is relatively expensive.

[0003] There is therefore a need for apparatus which is suitable for connecting into a load circuit and which will switch on the load in response to the detection of an intruder or remotely transmitted signal, and which can be readily easily connected by a do-it-yourself enthusiast or handyman or the like. The present invention is directed towards providing such apparatus.

[0004] According to the invention, there is provided apparatus for switching a load circuit in response to an intruder or remotely transmitted signal being detected, the load circuit comprising a load fed through a switch, the apparatus being of the type comprising detecting means to detect an intruder or signal, short circuit means to short circuit the switch of the load circuit, the short circuit means being responsive to the detecting means, a power circuit to power the short circuit means and charging means to charge the power circuit, characterized in that the charging means comprising a pair of input terminals for connecting across the load switch and the charging means, in use, draws current from the load circuit across the load switch when the load switch is open.

[0005] The advantages of the invention are many. However, the most important advantage of the invention is the fact that the apparatus can be connected into the load circuit across the terminals of the load circuit switch. This, therefore, enables one with relatively no skill in the art of electricity to connect the apparatus into a load circuit.

[0006] In one embodiment of the invention, the charging means comprises a rectifier and voltage limiting means.

[0007] The advantage of this feature of the invention is that the apparatus can operate from an AC or a DC circuit and by virtue of the fact that voltage limiting means are provided, the circuit is ideally suited for use with electronic components.

[0008] In another embodiment of the invention, the power circuit comprises a capacitor charged by the charging means.

[0009] The advantage of this feature of the invention is that the apparatus can be used indefinitely without the need for maintenance, repair or servicing.

[0010] In another embodiment of the invention, the power circuit comprises a battery charged by the charging means.

[0011] The advantage of this feature of the invention is that it enables the use of a relay or the like or other components of relatively higher power requirements to be used in the circuitry of the apparatus.

[0012] In a further embodiment of the invention, the short circuit means is a relay, the relay contact of the relay being connected across the switch of the load circuit, the relay being powered by the power circuit.

[0013] The advantage of this feature of the invention is that a relatively simple and inexpensive apparatus is provided.

[0014] Preferably, a timing circuit is provided to hold in the relay for a predetermined period of time after detection of an intruder.

[0015] The advantage of this feature of the invention is that it prevents the load circuit being switched on and off intermittently as an intruder is at the periphery of the range of the detector moving into and out of the range.

[0016] Advantageously, the detecting means comprises an infra-red detector.

[0017] The advantage of this feature of the invention is that a relatively sensitive apparatus is provided which, in general, is not prone to giving false alarms.

[0018] In another embodiment of the invention, a light sensing means is provided to prevent the short circuit means being activated in the event of the light sensing means sensing light.

[0019] The advantage of this feature of the invention is that it avoids unnecessary use of the apparatus, thereby conserving power in the power circuit.

[0020] Further, the invention provides a load circuit comprising a load and a switch in series with the load to switch the load, and the apparatus according to the invention, the apparatus according to the invention being connected across the terminals of the switch in the load circuit.

[0021] The advantage of this feature of the invention is that it provides a relatively simple, easily installed and relatively inexpensive arrangement.

[0022] Additionally, the invention provides a method for switching a load circuit in response to an intruder or a remotely transmitted signal being detected, where the load circuit comprises a load fed through a switch, the method comprising the steps of short circuiting the load switch by a short circuit means, powering the short circuit means from a power circuit and charging the power circuit from the load circuit by a drawing power from the load circuit across the terminals of the load switch when the switch is open.

[0023] The advantage of this feature of the invention are many, and in particular the advantage of the invention is that it permits the use of apparatus and the installation of the apparatus by a relatively inexperienced person.

[0024] The invention will be more clearly understood from the following description of some preferred embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic representation of circuitry of apparatus according to the invention illustrated connected into a load circuit,

Figs. 2(a) and (b) are circuit diagrams of the apparatus of Fig. 1, and

Figs. 3(a) and (b) are circuit diagrams of apparatus according to another embodiment of the invention.

[0025] Referring to the drawings, and initially to Fig. 1, there is illustrated a load circuit indicated generally by the reference numeral 1, which comprises a filament lamp 2, which is activated by a toggle switch 3. The filament lamp 2 and switch 3 are connected across a 220 volt AC supply by terminals 5 and 6. In this case, the filament light is a quartz halogen light of the type which would be typically used for perimeter lighting of a building compound or the like. Such lights are normally mounted around the outer walls of the building, or on high mast poles mounted in the compound, and the switch may be provided outside adjacent the light, or indeed, may be provided inside in a building. Needless to say, the circuit 1 could be an ordinary light and switch circuit inside a room or office of a building.

[0026] Apparatus 7 also according to the invention for activating the filament lamp 2 in response to the detection of an intruder or a remotely transmitted signal is illustrated in schematic representation in Fig. 1 connected into the load circuit 1. The circuitry of the apparatus 7 is illustrated in Fig. 2, and this will be described in detail below. The apparatus 7 comprises a detecting means, namely a pyro-electric detector 8 to sense infra-red radiation of an intruder at the perimeter of a building or about to enter the perimeter of a building, compound or the like. A short circuit means to short circuit the load switch 3 of the load circuit 1 is provided by contacts 9 of a relay RL1. The contacts 9 of the relay RL1 are connected across the switch 3 by terminals 10 and 11 which extend from the apparatus 7. A control circuit 14 controls the operation of the relay RL1 by powering the coil 15 of the relay RL1. The control circuit 14 activates the relay RL1 in response to the detector 8 sensing the presence of an intruder or remotely transmitted signal. A power circuit 16 powers the control circuit 14 and the relay coil 15. Charging means described with reference to Fig. 2 below are provided in the power circuit 16 for charging the power circuit 16. The charging means draws power from the load circuit 1 across the terminals of the load switch 3 through the terminals 10 and 11 when the switch 3 and the contacts 9 of the relay RL1 are open.

[0027] The detector 8, the relay RL1, the control circuit 14 and the power circuit 16, as well as the charging means are all mounted in a housing (not shown) which is provided with the two terminals 10 and 11 for connection across the switch 3.

[0028] Thus, the apparatus 1 may be connected into the loading circuit 1 by connecting the terminals 10 and 11 across the terminals of the switch 3. No other connections are required. This has the particular advantage of enabling a do-it-yourself enthusiast or handyman to connect the apparatus 7 into a load circuit 1 without the need of having skill in the art of electricity.

[0029] Referring now to Figs. 2(a) and (b), the circuitry of the apparatus 7 will now be described in detail. The circuit of Fig. 2(a) is connected to the circuit of Figs. 2(b) through the connection a to e of Figs. 2(a) and (b). The power circuit 16 comprises a 9 volt rechargable battery B1 and a storage capacitor C3 of 220 microF which power the coil 15 of the relay RL1 through a second switch means, in this case an NPN transistor TR5. The base of the transistor TR5 is controlled by the control circuit 14 under the control of the detector 8. This is described below. The power circuit 16 derives a power supply across the contacts of the switch 3 of the load circuit 1 when the switch 3 is open through the terminals 10 and 11. Power is fed through a charging means. namely a charging circuit 13 comprising a choke coil L1 and a capacitor C1 of 1 microF, and a resistor R40 of 2.2 Mohms which limit the voltage derived across the switch 3. The choke coil L1 also prevents noise or spikes from the load circuit 1 passing into the circuitry of the apparatus 7 resulting from switching of the switch 3 or the relay contacts 9. A half-wave rectifier provided by a diode D2 delivers a DC voltage to the power circuit 16 for powering the control circuit 14 and charging the battery B1 and the capacitor C3. A voltage limiting means, in this case a zener diode ZD1 holds the voltage being delivered to the power circuit at approximately 14 volts. A current sink resistor R1 of 10 Kohms sinks excessive current to the terminal 11. A diode D3 prevents the battery B1 discharging through the capacitor C3. A resistor R2 of 220 ohms limits the charging current to the battery B1, and a diode D5 prevents reverse feeding of the battery B1.

[0030] The capacitor C3 powers the coil 15 of the relay RL1 through a diode D4 when the transistor TR5 is switched on. The capacitor C3 provides the initial power required to close the contacts 9 of the relay RL1. A diode D9 connects the transistors T5 to ground. The battery B1 powers the coil 15 of the relay RL1 through a resistor R3 of 220 ohms to hold the contacts 9 closed when the switch 3 is short circuited by the relay contacts 9. In this condition, the voltage across the terminals 10 and 11 is zero volts.

[0031] The control circuit 14 is fed with a voltage Vc of approximately 5 volts which is regulated by a voltage regulator VR1. Power is delivered to the voltage regulator VR1 from the battery B1, and, when the switch 3 and contacts 9 of the relay RL1 are open, from the terminals 10 and 11. When the switch 3 is short circuited, the regulator VR1 is fed only by the battery B1. The voltage regulator VR1 is fed through a circuit 17. However, before describing the circuit 17 in detail, the detector 8 and control circuit 14 will first be described.

[0032] The detector 8 in this case as mentioned above is a pyro-electro infra-red detector 8, which includes a field effect transistor TR8 which is connected to the control circuit voltage Vc and ground through resistors R8 and R9 of 1 Kohm and 47 Kohms respectively. Capacitors C6 and C8 of respectively 100 microF and 10 nF form a low pass filter to filter noise to ground. The output of the detector 8 on pin 18 is connected through a two stage amplifier comprising stages 19 and 20 formed by an integrated circuit IC1 into comparators 21 and 22 also provided by the integrated circuit IC1. A DC blocking capacitor C12 of 1 microF connects the output pin 18 of the detector 18 to an input pin 12 of the amplifier 19. A potential divider formed by resistors R10 and R11 holds the pin 12 normally at about 2 volts. A noise decoupling capacitor C19 of 10 nF is connected across the resistor R11. The other input pin 13 of the amplifier 19 is held at a voltage below pin 12 by decoupling capacitors C7 and C20 both of 10 microF and a resistor R13 of 47 Kohms connected to ground. A resistor R12 of 2.2 Mohms and a capacitor C8 of 4.7 nF provide a feedback loop from the output pin 14 of the amplifier 19 to the pin 13. The output pin 14 of the amplifier 19 is connected to an input pin 9 of the amplifier 20 through a DC blocking capacitor C9 of 10 microF and a resistor R14 of 47 Kohms. A decoupling capacitor C21 of 10 nF connects pin 9 to ground. The second input pin 10 of the amplifier 20 is connected to a potential divider comprising resistors R15 and R16 of 3.3 Mohms and 2.2 Mohms respectively hold the input pin 10 in its normal state at about 2 volts. A decoupling capacitor C22 of 0.1 nF is connected to ground across the resistor R16. Thus pin 10 is normally high relative to pin 9. A feedback loop comprising a capacitor C10 of 4.7 nF and a resistor R17 of 1.5 Mohms connects the output pin 8 of the amplifier 20 to the input pin 9.

[0033] The output from the second stage amplifier 20 is fed through a DC blocking capacitor C11 of 10 microF into the input pins 3 and 6 of the comparators 21 and 22 respectively also provided by the integrated circuit IC1. The input pins 3 and 6 are normally held at approximately half the control voltage Vc by a potential divider comprising resistors R18 and R19 of 330 Kohms each. The second input pin 2 of the comparator 21 is normally held lower than the input pin 3 by a potential divider comprising resistors R20 and R21 of 390 Kohms and 330 Kohms respectively, while the input pin 5 of the comparator 22 is normally held higher than the input pin 6 by a potential divider comprising resistors R22 and R23 of resistors of 330 and 390 Kohms respectively. Accordingly, the comparator 21 detects the negative going leg of the output signal from the second stage amplifier 20, while the comparator 22 detects the positive going leg of the signal. The output pins 1 and 7 of the comparators 21 and 22 are normally high. However, on the detector 8 detecting an infra-red signal, the output signal on the pin 18 from the sensor 8 is amplified in the two stages 19 and 20 of the amplifier and the amplified output signal on being applied to the input pins 3 and 6 of the comparators 21 and 22 cause the output pins 7 and 1 to go low. This switches on the transistor TR5 which will now be described.

[0034] The base of the transistor TR5 is connected through a resistor R31 of 2.7 Kohms to the output pin 1 of a comparator 23. The reference input pin 3 of the comparator 23 is normally held high relative to the input pin 2 by a potential divider comprising resistors R27 and R28 of 100 Kohms and 220 Kohms respectively. The input pin 2 to the comparator 23 is connected through diodes D6 and D7 and resistors R24 and R25 of 56 ohms to the output pins of the comparators 22 and 21 respectively. A timing circuit 24 which comprises a capacitor C13 of 470 microF, a resistor R26 of 10 Kohms, and a variable resistor P1 of 2.2 Mohms is connected to the pin 2 of comparator 23. Depending on the time constant of the timing circuit 24, the capacitor C13 charges up and remains charged, while the outputs of the comparators 21 and 22 remain high. On a signal being received from the detector 8, the outputs of comparators 21 and 22 go low, thereby causing the capacitor 13 of the timing circuit 24 to discharge through the diodes D6 and D7. This causes the voltage on the pin 2 of the comparator 23 to pass over the voltage on the pin 3, thus causing the output pin 1 of comparator 23 to go high. This applies a high to the base of the transistor TR5 which in turn switches it on, to activate the relay coil 15. When the detector 8 ceases to detect the infra-red signal, the output signal on the pin 18 from the detector 8 disappears. This causes the outputs of the comparators 21 and 22 to go high again. However, the pin 2 of comparator 23 will remain low until the capacitor C13 has charged up again, thus holding the transistor TR5 switched on. Once the capacitor C13 has charged up, and the outputs of the comparators 21 and 22 remain high, the transistor TR5 is switched off. If however, the detector 8 detects further infra-red signals, a signal again is placed on the pin 18 which pulls the outputs of the comparators 21 and 22 low again. This thus causes the capacitor C13 to continue to discharge and the transistor TR5 is held on. Accordingly, the timing circuit 24 prevents the transistor switching on and off as an intruder is moving around the edge of the limit of the detection range of the detector 8. In practice it is envisaged that the variable resistor P1 will be set so that the time constant of the timing circuit is approximately 2 minutes.

[0035] A light sensing means is provided in the control circuit 14 to prevent the transistor TR5 switching on the relay RL1 during daylight hours or if the load switch 3 is closed. The light sensing means comprises a light dependent resistor OPR1 one terminal of which is connected to ground through a resistor R29 of 100 Kohms and an NPN transistor TR4 as will be described below. The other terminal of the light dependent resistor QPR1 is connected to the input pin 6 of a comparator 25. A potential divider comprising resistors R32 and R33 of respectively 220 Kohms and 470 Kohms hold the input pin 6 normally low relative to an input pin 5 of a comparator 25. The input pin 5 is normally held high by a potential divider comprising resistors R34 and R35 of 1.8 Mohms and 18 Mohms respectively. The output pin 7 of the comparator 25 is connected through a resistor R30 of 10 Kohms to the base of the transistor TR4. The transistor TR4 connects the input pin 3 of the comparator 23 to ground through a diode D11. Thus, when the transistor TR4 is switched on, the pin 3 of comparator 23 is grounded, and in this case the output of pin 1 of the comparator 23 remains low, irrespective of the condition of its input pin 2.

[0036] During daylight hours and while it is exposed to light, the resistance of the light dependent resistor OPR1 remains relatively low, thus the output from the comparator 25 remains high, and the transistor TR4 conducts to ground. This holds pin 3 of the comparator 23 low, and thus prevents a cross-over of voltage between the pins 2 and 3, thereby holding the output pin 1 of comparator 23 low. Thus, irrespective of whether the output pins 1 and 7 of the comparators 21 and 22 are high or low, the output pin 1 of comparator 23 will always remain low. During nightime the resistance of the light dependent resistor OPR1 goes high, this thus causes the output of the pin 7 of the comparator 25 to go low, thus switching off the transistor TR4. Accordingly, with the transistor TR4 switched off, the input pin 3 of the comparator 23 goes high, and on the outputs of the comparators 21 or 22 going low, pin 2 of comparator 23 similarly goes low, and accordingly, the output pin 1 of the comparator 23 goes high, thus switching on the transistor TR5. Similarly, if the filament lamp 2 is switched on by the switch 3, the light dependent resistor OPR1 senses this as being a daylight condition, and thus similarly holds the transistor TR5 off irrespective of the outputs of the comparators 21 and 22.

[0037] The circuit 17 will now be described. The output from the battery B1 and the power from the terminal 10 is fed through switch means, namely a PNP transistor TR1 into the voltage regulator VR 1. The transistor TR1 is activated by a second switch means, namely a NPN transistor TR2 which is connected to the base of the transistor TR1 through a current limiting resistor R4 of 10 Kohms. The base of transistor TR2 is connected through a current limiting resistor R37 of 100 Kohms to the half wave rectifier line input after the diode D2. Thus, once input power is on the terminal 10, the base of transistor TR2 is held high, thus switching it on, and connecting the base of TR1 to ground, which in turn switches on TR1. The base of transistor TR2 is also connected to the output pin 1 of the comparator 23. This ensures that TR2 will be held switched on when the relay contacts 9 of relay RL1 close. When the relay RL1 is closed, the potential across the contacts 9 of the relay RL1 falls to zero. While the relay contacts are closed, the transistor TR5 is conducting by virtue of the fact that its base is held high by the comparator 23 and thus pin 1 of comparator 23 is high. This high connected to the base of the transistor TR2 keeps the transistor TR2 conducting. This is essential, since if TR2 failed to conduct on the relay RL1 closing, TR1 would switch off and there would no longer be power from the battery to power the control circuit 14. Transistors TR1 and TR2 also prevent discharge of the battery B1 while the apparatus is being transported or stored prior to installation. A capacitor C4 holds the base of transistor TR1 low during the period while the contacts 9 are closing.

[0038] A low voltage protection circuit which prevents the transistor TR5 switching on should the battery voltage drop below normal is provided by transistors TR3 and TR6. Transistor TR3 is an NPN transistor and connects a resistor R7 of 100 Kohms to ground through a diode D10 and transistor TR2. The base of transistor TR3 is normally held at approximately +0.6 volts by means of a potential divider comprising resistors R5 and R6 of 1 Kohms and 5.6 Kohms respectively. On the voltage of the battery B1 dropping below its normal level, the voltage on the base of transistor TR3 drops below 0.6 volts, thus switching off transistor TR3. Transistor TR6 is shunted across the resistor R34 and a capacitor C14 of 100 microF. Transistor TR6 is an NPN transistor and its base is connected to ground through transistor TR3, diode D10 and transistor TR2. Thus, so long as the battery voltage B1 remains normal, the base of transistor TR6 is held at ground potential and the transistor TR6 is switched off. Once the battery voltage drops below normal, transistor TR3 switches off and a high is put on the base of transistor TR6, thus switching it on. This causes the pin 5 of the comparator 25 to go high, thereby holding pin 7 high. A high is thus put on the base of transistor TR4 to switch it on, thereby grounding the input pin 3 of comparator 23. As described above, once the pin 3 of comparator 23 is grounded, the output pin 1 remains low, thereby holding transistor TR5 switched off. This state continues until the battery voltages increases sufficiently to switch transistor TR3.

[0039] Capacitors C15, C16 and C17 are decoupling capacitors to stablise the voltage Vc.

[0040] A varistor V1 and capacitor C50 of 0.1 microF connected across the terminals 10 and 11 prevents voltage surges on the terminals 10 and 11 from damaging the components of the apparatus.

[0041] In use, the apparatus 7 is mounted on a wall of the perimeter of a building, compound or the like, so that the detector 8 can detect infra-red radiation from an intruder approaching or within the perimeter of the building or compound. The apparatus 7 is connected into the load circuit 1 with the terminals 10 and 11 of the apparatus 7 connected across the switch 3 of the circuit 1 as illustrated in Fig. 1. During daylight hours, and during nightime hours, when an intruder is not detected, the relay RL1 remains open.

[0042] In this state, and when the switch 3 is also open, the capacitor C3 charges and the battery B1 is charged. On detection of an intruder by the detector 8, the transistor TR5 is switched on, thus operating the relay RL1. The charge on the capacitor C3 gives the initial power required to pull in the contacts 9 of the relay and the battery B1 retains the relay RL1 closed while the intruder remains within range of the infra-red detector 8. The relay RL1 remains closed while an intruder remains within the range of the detector 8 or until the capacitor C13 in the timing circuit 24 charges up after the intruder has gone out of the range of the detector 8. Once the capacitor C13 has charged up, the transistor TR5 is switched off. Should the intruder remain, the capacitor C13 will not charge, and thus the transistor TR5 remains switched on, and the relay RL1 is held in. While the relay RL1 remains closed, the transistors TR1 and TR2 are held in their conducting mode by the high on the output of the comparator 23. Thus, the battery B1 retains the relay coil 15 activated to hold the contacts 9 of the relay RL1 closed. While the light dependent resistor OPR1 senses light, the transistor TR5 is held switched-off, irrespective of whether an intruder is detected.

[0043] Referring now to Figs. 3(a) and 3(b), there is illustrated a circuit diagram of apparatus according to another embodiment of the invention. This apparatus is substantially similar to that already described and is suitable for use with the load circuit 1. Components in the apparatus of Fig. 3 which are similar to the apparatus of Fig. 2 are identified by the same reference numerals. The circuits of Figs. 3(a) and 3(b) are connected at the points a, b, c, d and e.

[0044] The charging circuit 13, the power circuit 16 and the control circuit 14 of the apparatus of Fig. 3 are substantially similar to the respective circuits of Figs. 2(a) and 2(b). The power circuit 16 comprises a battery B1 and storage capacitor C3 similar to those of the power circuit 16 of the apparatus of Fig. 2. In this case, the relay is a latching relay of the type which only requires a single pulse to switch it on and a single pulse to switch it off. These relays will be well known to those skilled in the art. In this case, the relay RL1 has two coils 15a and 15b, the coil 15a switches the contacts 9 closed, while the coil 15b switches the contacts 9 open. In this case, the infra-red detector is similar to the detector 8 of the apparatus of the apparatus of Fig. 1 and on an intruder being detected, a high is placed at the point 100 in the control circuit 14. This point is similar to the input pin 2 of the comparator 23 of the apparatus of Fig. 2. The point 100 is connected through a resistor R100 of 10 Kohms to the input pin 1 of an inverter U1.

[0045] A low on the input pin 1 puts a high on the output pin 2 of the inverter U1. The output pin 2 of the inverter U1 is connected to an input pin 3 of an inverter U2 through a capacitor C100 of 0.1 microF. Thus, on a high being placed on pin 2 of the inverter U1, a positive going pulse appears on the input pin 3 of the inverter U2. This in turn puts a negative going pulse on the base of a PNP transistor TR100 switching it on momentarily. A current limiting resistor R101 of 10 Kohms is connected between the inverter U2 and the base of the transistor TR100. While the transistor TR10 is switched on a high is placed on the base of an NPN transistor TR101 through a resistor R102 of 2.2 Kohms, thus switching on the transistor TR101 for the duration of the pulse. This connects the on coil 15a of relay RL1 to ground, thus powering the coil 15a to close the contacts 9 of the relay RL1. While a low remains at the point 100 in the circuit 14, the output pin 2 of the inverter U1 remains high. This thus keeps a high on the base of transistor TR2, keeping the transistor TR1 switched on and accordingly the battery B1 powers the control circuit 14.

[0046] On the point 100 going high, a low is placed on the output pin 2 of the inverter U2, which places a negative going pulse on an input pin 5 of an inverter U3 which is connected to the inverter U1 through a capacitor C101 of 0.1 microF. The negative going pulse causes a positive going pulse on the output pin 6 of the inverter U3 which switches on an NPN transistor TR102 for the duration of the pulse. For the duration of the pulse, the off coil 15b of the relay RL1 is powered, thereby opening the contacts 9 of the relay RL1. Thus, on an intruder being detected, the on coil 15a is pulsed closing the relay contacts 9, and on an intruder moving out of the range of the infra red detector 8 and the timer circuit 24 having timed out, the off coil 15b of the relay RL1 is pulsed, thereby opening the contacts 9 of the relay RL1.

[0047] The low voltage detecting circuit 17 in this case also comprises a transistor TR3 which is fed across a divider comprising resistors R5 and R6. On the voltage of the battery B1 dropping below a predetermined level, the transistor TR3 is switched off. This thus puts a high on the input pin 19 of an inverter U4 through a resistor R103 on 100 Kohms. The output pin 18 of the inverter U4 goes low. The inverter U4 is connected to an inverter U5 through a diode D99 and a resistor R99 of 100 ohms. The low on the output pin 18 of the inverter U4 brings the input pin 13 of the inverter U5 also low, thus putting the output pin 12 of the inverter U5 high. The high on the pin 12 of the inverter U5 puts a high on the input pin 1 of the inverter U1 through a diode D101, thereby preventing the input pin 1 going low in the event of an intruder being detected. This thus prevents the circuit operating in the event of a intruder being detected. Furthermore, the presence of the high on the inverter U1 also pulses the off coil 15b of the relay RL1, thereby opening the contacts 9. The charging circuit 13 can then charge up the battery B1, provided, of course, that the switch 3 of the load circuit 1 is open. The input pin 5 of the inverter U3 is connected through a diode D100 to the output pin 18 of the inverter U4, which further ensures that the input pin 5 of the inverter U3 is held low to prevent the relay being switched on.

[0048] When the battery voltage goes above the minimum predetermined level, the transistor TR3 switches on, thereby connecting the input pin 19 of the inverter U4 to ground. This puts the output pin 18 of the inverter U4 high. However, the input pin 13 of the inverter U5 will not go high until a capacitor C105 of a timing circuit comprising the capacitor C105 and a resistor R105 has charged up through the resistor R105. On the capacitor C105 having charged up, the pin 13 of the inverter U5 goes high. This puts a low on the output pin 12 on the inverter U5, removing the high from the input pin 1 of the inverter U1. Accordingly, until the capacitor C105 has charged the input pin 1 of the inverter U1 is held high, holding the apparatus disabled. This gives the battery time to charge above its minimum level. In practice, it is envisaged that the capacitor C105 and resistor R105 will be sized to give the timing circuit a timing constant of about four to five minutes. In this particular embodiment of the invention, resistor R105 is of 560 Kohms. Accordingly, once the high has been removed from pin 1 of the inverter U1, on the infra red detector 8 detecting an intruder, the pin 1 of the inverter U1 is brought low, thereby causing the contacts 9 of the relay RL1 to close.

[0049] To prevent the apparatus operating during daylight or when the light 2 is switched on a light dependent resistor OPR100 is provided. The light dependent resistor OPR100 forms one resistor of a potential divider circuit comprising a resistor R106 of 220 Kohms. During daylight hours, the resistance of the light dependent resistor OPR100 remains relatively low, thereby putting a low on the input 1 of an inverter U6. This puts a high on the output pin 2 of the inverter U6, which is connected through a diode D106 to the input pin 1 of the inverter U1. This thus ensures that the relay contacts 9 will remain open. During nighttime hours, or when the light dependent resistor OPR100 is deprived of light, its resistance goes high, thereby allowing the input pin 1 of the inverter U6 to go high, and the output pin 2 of the inverter U6 to go low. This removes the high from the input pin 1 of the invert U1, thus allowing the circuit to operate on an intruder being detected by the infra-red detector 8. To prevent the apparatus switching off the light 2 on the light dependent resistor OPR100 sensing the light 2, a high is fed through the diode D107 from the output pin 2 of the inverter U1 to the input pin 1 of the inverter U6. Thereby, the input pin 1 of the inverter U6 is held high irrespective of the resistance value of the light dependent resistor OPR100. This in turn keeps the output pin 2 of the inverter U6 low.

[0050] Otherwise, the operation of the circuit of the apparatus of Fig. 3 is similar to the operation of the circuit of the apparatus of Fig. 2.
It will be appreciated that while both circuits have been described as comprising a low voltage battery detection circuit, this, in certain cases, could be dispensed with. Needless to say, other suitable low voltage detection circuits could be used without departing from the scope of the invention. Furthermore, it will be appreciated that in certain cases, the daylight detection means comprising the light dependent resistor OPR1 may be dispensed with. Indeed, in certain cases other suitable daylight or light detection circuits could be used without departing from the scope of the invention.

[0051] Furthermore, it will be appreciated that while the output of the detector 8 has been described as being passed through a two stage amplifier, this is not necessary, it could be passed through any suitable amplifying means, and indeed, in certain cases, if the output signal from the detector 8 was sufficient without amplification, the amplifiers may be dispensed with. Further, it will be appreciated that in certain cases only one of the comparators 21 and 22 may be provided.

[0052] While the timing circuit 24 has been described as having a time constant of two minutes, any other suitable or desired time constant could be provided. Indeed, in certain cases, the timing circuit 24 may be dispensed with. While the time constant of the circuit comprising the resistor R105 and the capacitor C105 is 4 to 5 minutes, other suitable times could be provided.

[0053] While the circuitry has been fed from the terminals 10 and 11 through a half wave rectifier, in certain cases, if desired, a full wave rectifier could be provided. Needless to say, any other suitable charging circuit for the battery could be used, and in certain cases, the capacitor C3 may be dispensed with. In certain cases, the battery may be dispensed with.

[0054] It is also envisaged in certain cases that the transistors TR1 and TR2 may be dispensed with. In particular, these could be dispensed with if the apparatus were sold without a battery in place.

[0055] It will of course be appreciated that many other suitable values of components besides those described could be used without departing from the scope of the invention.

[0056] It will also of course be appreciated that other suitable switching means besides a transistor for switching on the coil or coils of the relay could be provided instead of the transistor TR5 or TR100, TR101 and TR102.

[0057] It is also envisaged that while the apparatus has been described for connecting into a load circuit powered by 220 volts, it could be used in connection with a load circuit powered by any other voltage, whether AC or DC. Where the load circuit is powered by a lower or higher voltage, the inductance L1 and capacitor C1 may be replaced by an inductance and capacitor of more appropriate values or they may be dispensed with. Furthermore, where the load circuit is powered by a DC voltage supply, then the capacitor C1 and inductance L1 may be dispensed with, as may the rectifier be dispensed with.

[0058] While the short circuit means has been described as being provided by a relay, other suitable short circuit means could be provided. For example, in certain cases, it is envisaged that a Triac, Diac or the like may be provided. It is also envisaged that other suitable means for regulating the voltage supply to the control circuit could be provided without departing from the scope of the invention.

[0059] Further, other suitable detecting means besides an infra-red detector could be used. Where an infra-red detector is used, it could be an active or passive detector. It is also envisaged that while the apparatus has been described for detecting an intruder, it could also be used for detecting a remotely transmitted signal, such as, for example, a radio signal or any other remotely transmitted signal. In which case, appropriate detecting means would be provided. Needless to say, where the apparatus is for use for detecting an intruder, any other suitable detector could be used besides an infra-red detector. For example, an ultra-sonic detector, an inertia sensor or the like.

[0060] Further, while apparatus has been described for switching a load in a load circuit where the load is provided by a filament lamp, it could be used for switching any type of load, for example, an alarm, or any other type of load circuit. However, it is important that the load should not present an open circuit when switched off.

[0061] Further, it is envisaged in certain cases that the apparatus could also house the switch of the load circuit. In which case, the apparatus and load circuit switch would be provided as a single integral unit.

[0062] It will of course be appreciated that instead of a single filament light, many lights could be activated by the apparatus across a single load switch.

[0063] In certain cases, it is envisaged that the apparatus could be powered exclusively by one or more storage capacitors. In particular, it is envisaged that the apparatus with the latching relay illustrated in Figs. 3(a) and 3(b) could relatively easily be powered with the capacitors without the need for a rechargable battery.

Claims

1. Apparatus for switching a load circuit (1) in response to an intruder or remotely transmitted signal being detected, the load circuit comprising a load (2) fed through a switch (3), the apparatus being of the type comprising detecting means (8) to detect an intruder or signal, short circuit means (RL1) to short circuit the switch (3) of the load circuit (1), the short circuit means (RL1) being responsive to the detecting means (8), a power circuit (16) to power the short circuit means (RL1) and charging means (14) to charge the power circuit (16), characterized in that the charging means (14) comprising a pair of input terminals (10,11) for connecting across the load switch (3) and the charging means (14), in use, draws current from the load circuit (1) across the load switch (3) when the load switch (3) is open.

2. Apparatus as claimed in Claim 1 characterised in that the charging means (14) comprises a rectifier (D2) and voltage limiting means (ZD1).

3. Apparatus as claimed in Claim 1 or 2 characterised in that the power circuit (16) comprises a capacitor (C3) charged by the charging means (14).

4. Apparatus as claimed in any preceding claim characterised in that the power circuit (16) comprises a battery (B1) charged by the charging means (14).

5. Apparatus as claimed in Claim 4 characterised in that the short circuit means (RL1) is a relay (RL1), the relay contact (9) of the relay (RL1) being connected across the switch (3) of the load circuit (1), the relay (RL1) being powered by the power circuit (16).

6. Apparatus as claimed in Claim 5 characterised in that a timing circuit (24) is provided to hold in the relay (RL1) for a predetermined period of time after detection of an intruder.

7. Apparatus as claimed in any preceding claim characterised in that the detecting means (8) comprises an infra-red detector (8).

8. Apparatus as claimed in any preceding claim characterised in that a light sensing means (OPR1) is provided to prevent the short circuit means (RL1) being activated in the event of the light sensing means (OPR1) sensing light.

9. A load circuit (1) comprising a load (2) and a switch (3) in series with the load (2) to switch the load (2), and apparatus (7) according to any of Claims 1 to 8 characterised in that the apparatus (7) is connected across the terminals of the switch (3) in the load circuit (1).

10. A method for switching a load circuit (1) in response to an intruder or a remotely transmitted signal being detected, where the load circuit (1) comprises a load (2) fed through a switch (3), the method comprising the steps of short circuiting the load switch (3) by a short circuit means (RL1), powering the short circuit means (RL1) from a power circuit (16) and charging the power circuit (14) from the load circuit (16) by a drawing power from the load circuit (1) across the terminals of the load switch (3) when the switch (3) is open.

Drawing