WO2002013387A1

WO2002013387A1 - Switch assembly

Info

Publication number: WO2002013387A1
Application number: PCT/GB2001/003603
Authority: WO
Inventors: Colin Botting
Original assignee: Herga Electric Limited
Priority date: 2000-08-09
Filing date: 2001-08-09
Publication date: 2002-02-14
Also published as: GB0019616D0; WO2002013387A8; GB2366080A; AU2001278591A1

Abstract

There is described a switch assembly comprising a control element (2) for mounting to one face of a solid panel (1) and a switching element (3) for mounting to the other face of the panel. The control element contains a movable magnet, a parameter of whose field is detected by a sensor in the switching element to provide an electrical switching output in dependence on the field parameter sensed.

Description

Switch Assembly

The present application relates to switching apparatus for controlling electrical circuits, and is particularly concerned with switches for use in controlling electrical appliances and machinery.

Switches for controlling machinery and appliances are frequently mounted to control panels, with the electrical switching components mounted behind the panel, and a control element positioned on the front of the control panel . An opening is formed in the panel so that a mechanical connection can pass through the panel to link the control element with the switching components. Positioning the switches on the control panel will involve forming an array of openings in the panel . Not only is the forming of these openings a time-consuming operation, but it also fixes the positions of the switches on the panel preventing any subsequent adjustment of the switch positions.

Proposals have been made in the prior art for switch assemblies in which a control element is mounted to one face of a control panel and a switching element is mounted to the other face of the control panel, and wherein the connection between the control element and the switching element is made by non-mechanical means . In this way, the need to form openings in the panel is avoided. The cost of producing the panel is thus reduced, and the possibility of repositioning the switches without modifying the panel is also afforded.

In U.S. patent 5920131 there is described a switch assembly for controlling an electric cooker hob having a glass top panel, wherein a switching element mounted beneath the panel incorporates a light source and light sensors, and a control element mounted above the panel includes a fibre-optic element which collects light from the light source and directs light to a selected one of the light sensors, depending on a rotary position of the control element. Such an arrangement is clearly only suitable for use with panels formed from translucent or transparent materials.

In an alternative proposal for a switching assembly for a control panel, as illustrated for example in German patent 4432399, a control element mounted above a panel incorporates a permanent magnet, and a switching element mounted below the panel incorporates a plurality of magnetically-operated switches . When the permanent magnet is positioned adjacent one of the switches, its switching state changes and control of the appliance is affected on the basis of these changed switching states. The magnetic field of the permanent magnet is used to move a mechanical component in the switching element so as to change the switching state. Examples of such magnetically-operated switching elements are reed switches. While this arrangement can provide a switch assembly usable on an opaque panel, the operation of the switching element depends on a sufficient magnetic field strength to move its mechanical components, and thus the strength of the permanent magnet must be related to the thickness of the panel on which the switch assembly is to be mounted so as to ensure that the spacing between the control element and the switching element does not exceed the capability of the magnet to operate the switching element. A disadvantage of this type of switch is that the point in the range of movement of the control element at which the switching element changes state is dependent on the thickness of the panel, since it is the panel thickness which governs the magnetic field strength which causes movement of the mechanical components of the switching element.

An objective of the present invention is to provide a switching assembly for use with a control panel which requires no opening to be formed in the control panel, and which can be used with a range of panel materials and thicknesses .

A further objective of the present invention is to provide a switching assembly for mounting to a panel, in which movement of a control element from one end to the other of a path of travel causes a change in state in a switching element at a predetermined point along the path of travel . A yet further objective of the present invention is to provide a switching assembly comprising a control element for mounting to one face of a control panel and a switching element for mounting to the other face of a control panel, the control element incorporating a permanent magnet and the switching element comprising a magnetic field sensor for detecting a change in magnetic flux caused by movement of the control element, and a controller for outputting a switching signal on the basis of the detected change in magnetic flux.

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a first embodiment of a switch assembly according to the invention;

Figure 2 is a diametral sectional view of the switch assembly of Figure 1;

Figure 3 is a schematic circuit diagram of the circuitry within the switching element;

Figure 4 is a flow chart showing a first mode of operation of the controller of the switching element;

Figure 5 is a flow chart showing a second mode operation of the controller of the switching element; Figure 6 is a sectional view of a second embodiment of the switch assembly, showing the operating element in a first switching position;

Figure 7 is a view similar to Figure 6 , showing the switching element in a second switching position;

Figure 8 is a schematic sectional view of a third switch assembly of the present invention; and

Figure 9 is a circuit diagram of a further embodiment of the sensor element incorporating a timer circuit and relay.

Referring now to the drawings, Figure 1 shows a schematic view of the switch assembly applied to a panel 1 such as a horizontal worktop panel for a kitchen. In the illustration, the worktop panel is shown as a wooden panel, but it is to be understood that the worktop panel may be of plastics material, natural or reconstituted stone, of metal, or any other suitable material. In the case of a metal panel, the thickness of the panel may be considerably less than the thickness of the wooden panel shown. It is further to be understood that the panel need not be a horizontal worktop, but may be a vertical or inclined control panel surface.

Mounted to the upper surface of the worktop panel 1 is a control element 2 , and mounted beneath the worktop panel 1 is a switching element 3. The structure of the control element 2 is more clearly seen in Figure 2.

The control element 2 comprises a base 4 which is fixed to the worktop 1 by an adhesive layer 5. The adhesive layer may be applied directly to the base 4, or may be constituted by a double-sided adhesive tape . In a preferred embodiment, the underside of the base 4 has an adhesive layer applied thereto, and a release liner the applied over the adhesive layer. To fix the base to the worktop 1, the release liner is peeled off the adhesive layer, and the adhesive layer is pressed onto the worktop 1 in the required position.

The base 4 is generally circular in plan, and has a central upstanding stud 6 which acts as a spindle for a rotating control wheel 7. The stud 6 has a bifurcated upper end comprising two tines, each tine having an abutment surface facing towards the base 4, and a tapered lead-in surface facing away from the base 4.

The control wheel 7 has a central part formed with a bore 8 with an enlarged counterbored upper part 8a. A disc 7a extends radially outwardly from the central part of the control wheel, and a downturned peripheral flange 7b extends toward the worktop 1 , and surrounds the base 4. The upper surface of the disc 7 a has a recess formed therein to receive a cap 9. The cap 9 may carry indicia such as "On" and "Off" markings, or a circumferentially extending graduated scale.

To the underside of the disk 7a is attached a permanent magnet 10. In the embodiment shown, the magnet is a bar magnet, and is arranged to extend substantially radially of the disk 7a.

To assemble the control element, the magnet 10 is attached to the underside of the disk 7a, either by bonding or by providing the disk 7a with a clip or other formation capable of gripping and holding the magnet. The bifurcated end of the stud 6 is then introduced into the bore 8 of the control wheel 7, and pushed through the bore until the abutment surfaces of the tines can engage the counterbored upper part 8a. The cap 9 is then fixed in the recess, to conceal the bifurcated end of the stud 6 and to provide appropriate control markings for the control wheel 7.

The control element is then ready for attachment to the worktop 1, by bonding the underside of the base 4 to the worktop as described above. When the base is attached to the worktop, the control wheel 7 is a rotatable about the stud 6, and rotation of the control wheel 7 causes the angular orientation of the magnet 10 relative to the worktop 1 to change. Cooperating stop means (not shown) may be provided between the control wheel 7 and the base 4, to limit the extent of relative angular movement of the control wheel 7 and base 4. Preferably the angular movement allowed between the control wheel 7 and the base 4 is between 30 and 120 degrees.

The switching element 3 is a solid-state device comprising at least one magnetoresistive element 20, 21,

22, 23 whose resistance changes as a magnetic field in which the element is positioned alters in strength or flux direction, an amplifier 29 receiving an input signal from the magnetoresistive element, and a microprocessor 31 which receives an input signal from the amplifier 29 and outputs a switching signal at an output terminal 32. The switching element 3 may optionally be provided with an indicator lamp or LED 34 connected in series with a current-limiting resistor 35 between the earth rail 28 and the output terminal 32, so that the switching state of the switching element can be determined visually. The magnetoresistive element preferably comprises two pairs of magnetoresistive components 20, 23: 22, 21 connected in a bridge circuit.

Figure 3 shows the circuit diagram of the switching element 3. The switching element 3 seen in Figure 3 comprises four magnetoresistive components 20, 21, 22 and

23. Two of the magnetoresistive components 22 and 23 are shielded from the effects of external magnetic fields by magnetic shielding 24. The remaining two magnetoresistive components 20 and 21 are unshielded, and thus their resistances vary as a magnetic field in which they are placed varies in field strength or flux direction. A bridge circuit comprising an upper node 25 connected to a power rail 26 and a lower node 27 connected to an earth rail 28 has one arm comprising a shielded magnetoresistive component 22 and an unshielded magnetoresistive component 21, and the other arm comprising an unshielded magnetoresistive component 20 and a shielded magnetoresistive component 23. The midpoints of the arms are connected to the inputs of an amplifier 29 with a feedback resistor 30, and the amplifier 29 provides an analogue input to a microprocessor 31. The microprocessor may include an internal memory, or may be connected to an external memory or register 33 providing RAM and ROM memory functions .

The microprocessor 31 is programmed with a calibration mode and an operating mode, the programming instructions being stored either in the internal memory of the processor 31, or in a part of the external memory 33. A first example of the operation of the microprocessor 31 is illustrated by the flow chart of Figure 4.

In Figure 4, the processor is programmed with a calibration mode (Steps Cl to C5 ) and an operating mode (Steps 01 to 04). Each time power is supplied to the switching element, the processor enters the calibration mode. The control wheel 7 is moved by a user from the "Off" position through its range of travel to the "On" position, so that the effect of the magnetic field of the magnet 10 on the unshielded magnetoresistive components 20 and 21 varies, and the resistance of the components changes from its minimum to its maximum value.

After the power is turned on, the bridge circuit provides inputs to the amplifier 29 which then supplies an analogue output to the processor 31. The processor stores this analogue output in a register or memory 33 at Step CI.

The microprocessor 31 continues to monitor the analogue output of the amplifier 29 at Step C2, while the control wheel 7 is moved through its range of movement. At sampling intervals determined by a timer within the processor 31, the output voltage from the amplifier 29 is compared with the stored value in the register (Step C3) and if the output is greater than the stored value, then the stored value is replaced by the higher voltage value (Step C4). This sampling continues until the control wheel 7 is at its "On" position, and the output from amplifier 29 is at a maximum, and thus the stored value in the register corresponds to the maximum output of amplifier 29.

The processor then moves to Step C5 , in which a reference point is calculated from the stored maximum value. The reference point may be calculated by simply subtracting a predetermined amount from the maximum value, or by setting the reference point at a proportion of the maximum value. The reference point is then stored in memory 33, at Step C6.

The processor is programmed to remain in its calibration mode for a predetermined time after initial power-up, to give the user ample time to move the control wheel 7 through its range of travel. For example, the processor may enter its calibration mode on power-up, and after an interval of 15 seconds may then enter its operating mode. A longer interval may be provided, which may be useful if the power supply connection is positioned remotely from the switch location. If the operator does not move the control element fully to the "On" position, but stops short, then the processor stores in the memory 33 a value corresponding to the highest analogue input reached as the MAX value. Although this will be less than the maximum value achievable, the processor 31 will calculate a reference value based on this highest input.

When the processor then enters its operating mode, the output voltage from amplifier 29 is monitored by the processor 31 at Step 01. In Step 02, the voltage output of the amplifier 29 is compared with the stored reference point. If the monitored output is greater than the reference point, the microprocessor 31 provides an output signal at output terminal 32 corresponding to an "On" signal (Step 03). If the monitored output is less than the reference point, the microprocessor 31 provides no output signal at output terminal 32 corresponding to an "Off" signal (Step 04). The presence or absence of a signal at output terminal 32 may directly control an electrical load, or may be fed to a relay which in turn controls power supply to the load. The switching state of the output terminal 32 may be visually determined by inspecting the indicator lamp or LED 34. When an output signal is provided to the output terminal 32, the lamp or LED 34 will be lit, indicating that the switch is "On". When no output signal is provided to the output terminal 32, the lamp or LED 34 will be unlit, indicating that the switch is "Off".

An alternative mode operation is illustrated by the flow chart of Figure 5. The operation is a similar to that shown in Figure 4, in that the processor initially enters a calibration mode (Steps Cll to C18) on power-up, and subsequently enters an operating mode (Steps Oil to 014) .

In the calibration mode illustrated in Figure 5 , a memory 33 associated with the microprocessor 31 is provided to store a maximum and a minimum value of the analogue output of the amplifier 29. In Step Cll the initial value of the analogue output is stored in the memory 33 both as the maximum and the minimum value. In Step C12, the analogue output of the amplifier 29 is monitored and successive sampling intervals, and in Step C13 the monitored value is compared to the stored maximum value. If the monitored value is greater than the stored value, then in Step C14 the stored maximum value is replaced by the monitored value.

In Step C15, the monitored value is compared to the stored maximum value. If the monitored value is less than the stored value, then in Step C14 the stored minimum value is replaced by the monitored value.

In Step C17 a reference point is computed from the stored maximum and minimum values. The reference point may be the average of the maximum and minimum values, or may be a value between the maximum and minimum values which divides the difference between the two values in a predetermined ratio. In Step C18, the reference point is stored in the memory 33.

As before, the processor is programmed to remain in its calibration mode for a predetermined time after initial power-up, to give the user ample time to move the control wheel 7 through its range of travel. With the operation as shown in Figure 5, the user need not commence movement of the control element at an end of its travel. Calibration will be effectively achieved provided that the control element is moved to each end of its travel during the calibration mode.

The operating mode of the processor is essentially the same as described above, with the analogue output of the amplifier 29 being monitored in Step Oil, and in Step 012 the analogue output is compared with the stored reference point, and an output signal is provided to the output terminal 32 on the basis of the comparison.

In order to install the switching assembly, the switching element 3 is attached to the undersurface of the worktop 1 and the operating element 2 is attached to the upper surface of the worktop 1. To facilitate correct alignment of the two components, the switching element 3 may be provided on its outer casing with an indicator marking such as a line or arrow which indicates the orientation of the magnetoresistive array within the switching element. The user may be instructed to align the direction of this line or arrow with a particular radial direction of the control element. For example, installation instructions may include the steps of:

1. Ensuring that the control wheel 7 is rotated fully to the "off" position relative to the base 4;

2. placing the control element in the required position on the worktop upper surface, with the control wheel 7 in the desired angular alignment for the user; and

3. Positioning and fixing the switching element 3 beneath the worktop 1, with the alignment mark on the switching element 3 in a predefined relationship to the angular orientation of the control wheel 7. For example, the switching element 3 may be fixed so that a line on the casing of the switching element is parallel to a radius of the control wheel 7 extending from the centre of the control wheel to the "Off" marking on the control wheel .

The installer may then connect the power supply to the switching element 3 , which will initiate the calibration mode. The installer then rotates the control wheel 7 from the "Off" position to the "On" position, in order that the calibration sequence can be performed and the maximum (and possibly also minimum) output value of the amplifier 29 can be captured. The processor 31 then calculates the reference value of the amplifier output at which the switching state of the switching element 3 will change. The switching element is then ready to enter its operating mode.

Figures 6 and 7 show an alternative embodiment of the switch assembly, in which the switching element 40 is configured as a monostable two-position "rocker" switch. The switching element 40 comprises a housing 41 having a substantially rectangular base 42 and upstanding side and end walls 43 and 44 respectively. A rocker element 45 is a pivotally mounted between the sidewalls 43 for reciprocal rocking motion about a horizontal axis A. Mounted within the rocker element 45 is a permanent magnet 46.

A pillar 47 extends upwardly from the base 42 of the housing 41, and supports a keeper 48 of magnetic material that its upper end. The position of the keeper 48 is such that, when the rocker switch is in the position shown in Figure 6, the attraction between the magnet 46 and the keeper 48 retains the rocker element 45 in this position. The magnet 46 extends in a plane substantially parallel to that of the base 42 in this position.

As before, the switching element 40 is mounted to one side of a panel or worktop 49 by means of an adhesive, layer 50. Mounted below the panel 49 is a switching element which corresponds to the switching element 3 of the above-described embodiment.

To operate the switch, downward pressure is exerted on the left-hand end of the rocker element 45 (as seen in the Figures). When sufficient force is exerted to overcome the attraction between the magnet 46 and the keeper 48, the rocker element 45 rotates about the axis A to the position shown in Figure 7.

In the position shown in Figure 7, the magnet 46 is inclined relative to the base 42 of the housing 41 at an angle of approximately 50 degrees, and the attraction between the magnet 46 and the keeper 408 exerts a force on the rocker element 45 urging it to rotate clockwise (as seen in the Figure) back to the position shown in Figure 6. While an angular rotation of 50 degrees is shown between the positions of Figures 7 and 8, it is foreseen that a change in angle of as little as 10 degrees or less may provide sufficient change in the resistance of the magnetoresistive elements. The rotation of the magnet about axis A as the switch is moved between the positions of Figures 6 and 7 changes the direction of the magnetic field sensed by the magnetoresistive elements in the switching element 3, and thus the resistances of the unshielded magnetoresistive elements are varied. The analogue output from the amplifier 29 linked to the bridge circuit also varies between maximum and minimum values, which are sensed and stored by the microprocessor in the same way as is described in relation to the first embodiment. The microprocessor 31 calculates a reference point for the output value of the amplifier 29, and produces a switching signal at the output terminal 32 as before.

In an alternative embodiment of the rocker switch, a second pillar 47a and keeper 48a (shown in phantom line in Figure 7) may be provided at the left-hand end of the base 42, so that when the rocker element 45 is moved to the position shown in Figure 7 the attraction between the magnet 46 and the second keeper 48a holds the rocker element 45 in the position shown in Figure 7. The addition of this second pillar 47a and second keeper 48a provides a bistable rocker switch.

Figure 8 shows yet another embodiment of the control element. In Figure 8, the control element comprises a housing 61, a push-button element 62 movable vertically in the housing, and cooperating formations (not shown) prevent the push-button 62 from rotating relative to the housing 61 about a vertical axis.

A rotating disk 63 is mounted within the housing 61 for rotation about a vertical axis. The disk 63 is provided with one or more cam elements 64 which cooperate with cam elements 65 mounted on the push-button element 62, so that movement of the push-button element 62 towards the disk 63 causes rotation of the disk.

A spring 66 mounted to the disk 63 and the push-button element 62 urges the disk and the push-button element apart. The spring 66 may also apply a torque to these two components to maintain the cam elements 64 and 65 in engagement with each other, thus ensuring that as the push-button 62 is depressed the disk 63 rotates in a first angular direction, and when the push-button 62 is released the torsion in the spring 66 urges the disk 63 to return to its original angular position.

The disk 63 carries a bar magnet 67 extending diametrically of the disk 63.

The housing 61 is attached to a worktop or panel 68 as before, and a switching element 3 is attached beneath the worktop or panel 68 in alignment with the housing 61 of the control element. The calibration and operation of the switching element 3 are as described above, the switching element operating in response to the rotation of the magnet 67 from its rest position shown in Figure 8 to an angularly displaced position resulting from the action of the cam elements 64 and 65 when the push-button 62 is pressed.

In an alternative embodiment of the push-button type of control element described, latching elements may be provided between the disk 63 and the push-button 62 to provide an action wherein the push-button 62 remains depressed until a second pressure is applied to it, which releases the latch element.

Figure 9 illustrates schematically a circuit diagram for an alternative embodiment of the switching element. In Figure 9 parts corresponding to those shown in Figure 3 are given like reference numerals. In Figure 9, the switching element comprises a power rail and an earth rail, between which are connected in series a magnetoresistive element MRE and a fixed resistance R. The inputs of an amplifier 29 are connected respectively between the magnetoresistive element MRE and the fixed resistance R, and to the earth rail 28. The fixed resistance is preferably selected so that its resistance value lies between the resistance values of the magnetoresistive element when exposed to and shielded from a magnetic field, respectively. A feedback resistor Rl is connected between the amplifier output and the positive input of the amplifier 29.

The amplifier 29 provides an analogue input to be processor 31 which is linked to a memory 33. An output terminal 32 of the processor 31 provides a signal to a timer 51. The timer 51 is in turn connected to a relay 52, which has a pair of switched terminals 53 and 54. An electrical load is connected in series with the terminals 53 and 54, so that the power supply to the load can be controlled by the relay 52.

As the direction or field strength of a magnetic field in which the magnetoresistive element MRE is positioned changes, the resistance of that element changes and the voltage supplied to the positive input of the amplifier 29 varies. The voltage supplied to the negative input is constant, since the input is tied to the earth rail 28.

As before, the amplifier 29 provides an analogue input to the processor 31 which performs a calibration procedure as described above, and then enters an operating mode in which the analogue input is compared to a reference value and an output signal is provided to the timer 51 on the basis of this comparison. The timer 51 is arranged to switch the relay 52 to an "On" state when an output signal is received from the processor 31, and maintain that switching state for a predetermined time interval thereafter. The timer 51 is arranged to operate only when an output signal from the processor 31 is present, in order to provide a manual override facility. With this arrangement, when the control element is returned to the "Off" position, the analogue output from the amplifier 29 falls below the reference value and the output signal from the processor 31 ceases. The timer 51 is arranged then to return the relay 52 to the "Off" state, irrespective of whether the predetermined interval has elapsed or not.

The switching element illustrated in Figure 9 may be used, for example, to control a kitchen waste disposal unit, or other electrical appliance which should not be left running for a long period. The timer 51 may be arranged to operate the appliance for an interval of a few seconds, or for some minutes.

In the circuit illustrated in Figure 9, a voltage divider circuit is formed by the magnetoresistive element MRE and the fixed resistor R, to provide the varying voltage input to the amplifier 29. It will be appreciated that fixed resistances could be used in place of the two magnetically shielded magnetoresistive elements 22 and 23 in the bridge circuit of Figure 3, in order to reduce component costs .

In an advantageous modification of the calibration procedures described above, the processor 31 may be arranged to provide greater operator freedom by waiting, after the system is powered up, for a significant increase (for example 5% or more) in the analogue input to the processor before initiating the calibration procedure. The processor is programmed to enter the calibration mode after each "power on" is detected, but only after an increase in the analogue input has occurred. This modification provides the installer with greater facility for initially calibrating the switch, in that there is no time limit between power-up and the control element movement needed for calibration. Furthermore, if a power supply failure occurs, the processor will wait until the user first operates the control element after the power failure to perform a calibration and enter the operating mode. By programming the processor to await an increase in the analogue signal, the possibility that the control element is in the "On" position when the power failure occurs is dealt with. In such a situation, the processor will wait, after power is restored, until the operating element is returned to the "Off" position and then moved toward the "On" position. This latter movement provikes an increase in the analogue signal, and initiates the calibration sequence.

In the embodiments described above, the processor 31 is arranged to provide a switching output when the analogue input from amplifier 29 exceeds the reference value. It is to be understood that the processor may additionally or alternatively be provided with an output terminal providing an inverted output signal, i.e. providing an output only when the analogue input is less than the reference value. If both outputs (regular and inverted) are provided, the switch can be used to switch one load "Off" as it switches another load "On", and vice versa.

The present invention thus provides a switch assembly which can be mounted to a worktop or panel whose thickness lies within a wide range, without the switch assembly having to be factory-calibrated or otherwise modified to suit the particular thickness of panel to which it is to be attached. The switch assembly comprises a single magnet and a switching element which senses a change or a movement of the magnetic field associated with the magnet and provides an electrical switching output.

While the movement of the magnetic field described in the above embodiments is a rotation, it is foreseen that the switch assembly may include a switching element wherein a magnet is mounted to move along a rectilinear path. By suitable positioning of the switching element, the rectilinear movement of the magnet can provoke a change in the field strength and flux direction of the magnetic field at the switching element.

By suitable selection of the microprocessor 31, a plurality of magnetoresistive elements may be provided in common for a single processor. It is envisioned that a switching element may be provided wherein a plurality of magnetoresistive bridge circuits and their respective amplifiers are connected to a single processor having multiple output terminals. A plurality of control elements, possibly of different types, may then be mounted to correspond to the respective magnetoresistive circuits of the switching element.

Claims

1. An electrical switching assembly comprising: a control element comprising a permanent magnet movable between a first position and a second position; sensor means mountable within the magnetic field of the permanent magnet for sensing a parameter of the magnetic field associated with the permanent magnet; and control means for providing an electrical output signal on the basis of the sensed parameter.

2. An electrical switching assembly according to claim 1, wherein the sensing means comprises an element having an electrical parameter which varies with variations in a magnetic field, and the control means comprises means for comparing said electrical parameter with a reference value and means for providing an electrical output on the basis of the comparison result.

3. An electrical switching assembly according to claim 1 or claim 2, wherein the sensing means comprises a magnetoresistive component.

4. An electrical switching assembly according to claim 2 or claim 3, wherein the sensing means comprises a bridge circuit having first and second arms, each of the arms including a magnetoresistive component.

5. An electrical switching assembly according to claim 4 , wherein each arm of the bridge circuit comprises a magnetically shielded magnetoresistive component and an unshielded magnetoresistive component.

6. An electrical switching assembly according to claim 4, wherein each arm of the bridge circuit comprises a magnetically shielded magnetoresistive component and fixed resistor.

7. An electrical switching assembly according to claim 2 or claim 3 , wherein the sensing means comprises a voltage divider circuit comprising a magnetoresistive component and a fixed resistor connected in series.

8. An electrical switching assembly according to any of claims 2 to 7, wherein the control means comprises: means for storing a reference value; means for comparing an electrical output from the magnetoresistive component with said stored value; and means for providing a switching output on the basis of said comparison.

9. An electrical switching assembly according to any of claims 2 to 8, further comprising an amplifier for amplifying an electrical output of the magnetoresistive component.

10. An electrical switching assembly according to any preceding claim wherein the control means is operable in a calibration mode to detect a maximum sensed value for the parameter of the magnetic field and to determine and store a reference value on the basis of said maximum sensed value, and is operable in an operational mode to compare a sensed value of the parameter with said reference value and to provide a switching output on the basis of said comparison.

11. An electrical switching assembly according to claim 10 wherein the control means is operable in the calibration mode to detect maximum and minimum sensed values for the parameter of the magnetic field, and to determine and store a reference value on the basis of said maximum and minimum sensed values .

12. An electrical switching assembly according to any preceding claim, wherein the control element comprises: a planar base mountable to a supporting surface; a movable element mounted to the base for movement between first and second positions relative thereto; and a permanent magnet mounted to the movable element.

13. An electrical switching assembly according to claim

12, wherein the movable element is mounted to the base for rotary movement about an axis substantially perpendicular to the plane of the base.

14. An electrical switching assembly according to claim

13, wherein the permanent magnet is a bar magnet mounted substantially radially with respect to the rotation axis .

15. An electrical switching assembly according to claim 13 or claim 14, further comprising cooperating stop means formed on the base and on the movable element to limit the movement of the movable element relative to the base.

16. An electrical switching assembly according to any of claims 13 to 15, further comprising: a push-button element mounted for reciprocal movement towards and away from the base and including a first cam surface; a second cam surface associated with the movable element and engageable with said first cam surface; and the arrangement being such that movement of the push-button element towards the base causes rotation of the movable element in a first sense, and movement of the push-button element away from the base causes rotation of the movable element in a second sense opposite to the first.

17. An electrical switching assembly according to claim 16, further comprising releaseable latching means operable to retain the push-button element in its position adjacent the base.

18. An electrical switching assembly according to claim 12, wherein the movable element is mounted to the base for rotary movement about an axis substantially parallel to the plane of the base.

19. An electrical switching assembly according to claim 18, further comprising a keeper mounted to the base for engaging the magnet when the movable element is in its first position to retain the movable element in its first position.

20. An electrical switching assembly according to claim 19, further comprising a second keeper mounted to the base for engaging the magnet when the movable element is in its second position to retain the movable element in its second position.

21. A control element for an electrical switching assembly according to any preceding claim.

22. A method of controlling an electrical load comprising the steps of: mounting to one face of a panel a control element having a permanent magnet movable between a first position and a second position; mounting to an opposite face of the panel sensor means for sensing a parameter of the magnetic field associated with the permanent magnet; in a calibration mode, operating the control element to move the permanent magnet to its first position and its second position, sensing and storing a value for said parameter of the magnetic field at at least one of the first and second positions of the magnet, calculating and storing a reference value of the parameter on the basis of these stored value all values; and in an operating mode comparing the output of the sensor means with the stored reference value, and outputting a switching signal on the basis of the comparison.

23. A method according to claim 22, wherein the sensor means comprises a magnetoresistive element.

24. A data carrier carrying processor-implementable instructions for carrying out the calibration mode and operation mode steps of the method of claim 22 or claim 23.

25. A switching assembly for controlling and electrical load, substantially as described herein with reference to Figures 1 and 2 , Figure 3 , Figures 6 and 7 , Figure 8 or Figure 9 of the accompanying drawings.

26. A method of controlling an electrical load substantially as described herein with reference to Figure 4 or Figure 5 of the accompanying drawings .