GB2387721A

GB2387721A - A releasable magnetic electrical connector.

Info

Publication number: GB2387721A
Application number: GB0214071A
Authority: GB
Inventors: Joseph Gibson Dawson
Original assignee: MAGTRIX CONNECTORS Ltd
Current assignee: MAGTRIX CONNECTORS Ltd
Priority date: 2002-04-20
Filing date: 2002-06-19
Publication date: 2003-10-22
Also published as: GB0209097D0; GB0214071D0

Abstract

A method of electrically connecting and releasably attaching a first electrical device (2) to a second electrical device (2), so as to form an electrical circuit wherein one or more permanent magnets Fig 1 (4), each electrically and mechanically attached to either the first or the second electrical device, directly contact a magnetically attractable part of the other device so as to form an electrical connection by mechanically attaching one device to the other by magnetic attraction. The method is particularly suitable for attaching discrete electronics components (40 and 42) such as batteries and electrolytic capacitors to a circuit board (30).

Description

238772 1

ELECTRICAL CONNECTOR

The present invention relates to a method and devices for releasably attaching electrical components to and in electrical connection with another electrical device, such as a printed circuit board, by the use of one or more permanent magnetic devices.

Magnetic connectors for physical connection are widely known. GB 2071919 (Schluter) discloses a magnetic connector for ceramic tiles. GB 1589309 (Abe) discloses a magnetic sheet for releasably attaching doors, cladding and the like. GB 1530591 (Long) describes a cylindrical magnetic connector for connecting and securing a door in a doorframe wherein a connector magnet is optionally biased by a spring. GB 1 104933 (Clark) discloses a magnetic catch for a door wherein the catch is releasable by rotating a cylindrical magnet magnetically attached to another cylindrical magnet such that the magnets repel and the catch is released. None of the above references disclose the use of a releasably attachable magnetic connector for forming an electrical contact between electronic components.

Known methods of securing electrical and electronic components to printed circuit boards include soldering, clamping, push-fit connectors and a wide variety of clips.

The printed circuit board is the almost universally used vehicle for securing electronics components in a handleable physical, i.e. mechanical, form whilst placing them in working electrical contact. With increasing miniaturization of components applied to such circuit boards, mechanisms for releasably attaching components to circuit boards, as opposed to permanently soldering them in place, become increasingly delicate.

Mechanical clips, clamps and similar devices become increasingly difficult to manipulate manually when sub-miniature and miniature sizes are achieved. The users of such devices, especially when there is a requirement for repeated replacement and withdrawal of a component, run the risk of damaging an attached device or component during the manipulation of such delicate components. In addition stress fractures of printed circuit boards are a known problem particularly with spring loaded and latching connectors. Whilst this can be partially overcome by reducing the forces that such attachment means use to retain a component, this reduces the potential for securely holding such components, in for example, environments which will endure mechanical

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shock and vibration. There is therefore a need for a means of reieasably securing electrical components and in particular electronics components to other electronics components, such as a printed circuit board, in a simple, robust, reliable and yet miniaturized manner such that they may be releasably attached.

According to a first aspect of the invention there is provided a method of forming a releasable electrical connection, the method comprising the steps of: providing a first electrical device and a second electrical device; said first and second electrical devices being connected by at least one permanent magnet so as to form a releasable electrical connection therebetween.

The method may be used in the formation of an electrical circuit comprising the electrical connection so formed.

Due to increasing miniaturization, it is desirable that any method of releasably securing an electrical component also functions as a means of electrical connection to avoid wasting space. It is preferable that such methods of attachment for electrical components directly engage an electrical contact. In addition, when releasably securing components to a circuit board, if there is a difference between the means for making electrical contacts and the means for physically securing an electronics device, it is possible that such a device may be mechanically secured, but not in electrical contact.

Or alternatively the device can be in electrical contact, but not sufficiently well mechanically secured. It is therefore desirable to have an electrical contact for electronic components, in releasable association with a printed circuit board, which also achieves the physical retention of such electronics devices on the printed circuit board by the same means such that the integrity of mechanical connection is an indication of the integrity of electrical connection and vice versa.

The electrical devices of the method may be physically attached substantially by the releasable magnetic attachment.

Moreover, when mechanical electrical connectors are used for electronics components, repeated insertion and removal of such components leads to wear on the devices, particularly of mechanically interlocking parts, and thereby the potential for deterioration

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in any associated electrical contact. In particular, whilst plating such contacts with, for example, gold, can improve such contacts it is expensive to make a coating sufficiently thick that high numbers of repeat contacts may be made without wearing the coating away. There is therefore a need for a method of releasably attaching electrical components wherein the mechanical attachment does not comprise a mechanically interlocking component yet an electrical device is securely retained.

In addition it is desirable to decouple stresses placed on a circuit board by the insertion and removal or components and connectors. Whilst flexible couplings, such as wires my be used secure physical contact with a device to be connected is still required and such combinations take up additional space and increase complexity in manufacture There is therefore a need to make secure yet adjustable releasable connections to circuit boards.

The electrical devices of the method may optionally only be physically attached by releasable magnetic attachment. By combining physical securing and electrical contact means the 'real estate' of a printed circuit board may be conserved as is important in miniaturization. Also according to the method a permanent magnet comprising an electrical connection between the first and second device may be located on, i.e. attached, other than by means of magnetic attachment or attraction, to the first or second device Furthermore, the permanent magnet on the first device may directly physically and electrically contact the permanent magnet on the second device by means of magnetic attraction.

Releasably attached electrical devices of the method may be physically attached substantially by magnetic attraction. Releasably attached electrical devices of the method may be physically attached only by magnetic attraction. According to the method of the invention one or more points of magnetic attachment may participate in forming an electrical connection which is part of the electrical circuit. Primary physical and mechanical attachment of a magnet, i.e. attachment of a permanent magnet to that electrical device of which it is part, may be by any conventional mechanical securing means such as soldering, clamping and adhesion.

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It is an essential element of the invention that permanent magnets are in electrical connection with the electrical device secured by said magnet and may form an essential and integral part of an electric circuit so formed. It is therefore implicit in the invention that magnets will be arranged in the appropriate polarity to enable mechanical and electrical connection to occur, if appropriate to a given application. For the purposes of the invention electrical connection through a conductive surface coating, such as metal plating, of a magnetic substance of a magnet is an electrical connection with the magnet.

The two or more permanent magnets of the invention may all be primarily attached to one component only, for example a first electrical device. In such a case the other component, a second electrical device may have magnetically attractable electrical contact portions. Where the two or more permanent magnets of the invention may all be primarily attached to one component only, that component is preferably a printed circuit board. The method of the invention includes releasably magnetically attaching, and thereby forming an electrical connection between, a first electrical device and a second electrical device by means of a permanent magnet located on, i.e. attached to the first device. The first electrical device of the method of the invention may comprise a printed circuit board. The second electrical device of the method of the invention may also comprise a printed circuit board. The method of the invention may be used to releasably connect printed circuit boards together in electrical communication. Circuit boards may be readily changed with minimal mechanical abrasion of the electrical contact points giving the aforementioned advantages.

According to the method of the invention the permanent magnet on the first device directly physically and electrically contacts the permanent magnet on the second device by means of magnetic attraction. Since only magnets of opposite polarity will attract and readily contact one another the method provides a means for ensuring that incorrect connections are not made between electrical contacts thus avoiding any resultant damage. A wide range or electrical devices are suitable for use in the invention including fuses, batteries, button batteries, resistors, capacitors, lamps, and active components such as

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transistors and electrical sub-assemblies such as circuit boards, among others. The electrical devices may be electrical or electronic components. The electrical devices may be passive electronic devices in the form of discrete electronics components; such components may be capacitors, the capacitors may be ceramic or electrolytic capacitors.

Ceramic capacitors are preferably ceramic disc capacitors. Electrolytic capacitors are preferably axial electrolytic capacitors. The electrical devices may be surge arrestors, for the removal of voltage spikes in supply lines, preferably discrete surge arrestor components with a limited life-span. Exhausted components may therefore be conveniently replaced. It is preferable that electrical devices releasably mechanically attached using the invention are secured exclusively by surface portions, which are in electrical contact to form said electrical circuit. Mechanically interlocking means of securing the electrical device or devices may be absent other than any due to physical forces resulting from magnetic attraction and/or repulsion. Mechanical means for securing thereby excluded from optimal working of the invention may therefore include mechanically interlocking means such as latching, intermeshing, clips, screw threads and similar mechanical holding mechanisms. Mechanical guides, supports and the like which are secondary to the magnetic effect of releasable magnetic attachment may be used to help guide a component to the general area where the component is to be located but are not the primary medium of such attachment which, for uses within the scope of the invention, is dictated primarily by magnetic attachment. Devices for use in the invention therefore avoid the wear associated with a mechanically interlocking mechanism whilst retaining the inherent compactness of a method wherein the mechanical and electrical contact are achieved using the same means.

The second electrical device of the invention may be releasably magnetically attached between the two or more permanent magnets and comprise one or more discrete electronic components. Alternatively the second electrical device may consist solely of one or more discrete electronic components. The one or more discrete electronic components may be releasably physically attached by an attractive magnetic force between the permanent magnets so as to sandwich said components between the permanent magnets thereby holding them in place and in electrical contact. This provides a method of replaceably locating electrical components in an electrical device, such as a circuit board. A discrete component comprises an individual electrical function,

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such as a single resistor, as opposed to sub assemblies of multiple components, integrated circuits and the like.

The method may employ one or more discrete electronic components of consumable characteristics. Consumable characteristics are characteristics which are exhausted during use of the component. Examples include batteries, anti-voltage-surge devices.

Such devices are advantageously replaceable during the life of a piece of electrical equipment and the benefits of the invention of easy and repeatable replaceability are more fully utilizable. The second electrical device may comprise one component, particularly when the component is one of consumable characteristics. Any failure of such a device when the consumable characteristics are consumed is therefore limited to a single readily replaceable component.

The method may employ a number of discrete components used together sandwiched between So or more magnets preferably without a circuit board or other connecting means save for direct contact between components. Thereby, by for example, sandwiching various resistors, capacitors and other discrete components between a pair of magnets a compound device may be readily obtained and modified. Other examples include a battery and resistor, or a battery and a diode, by example. However, the method may employ a single discrete component.

In particular it is often desirable to adjust the values of electronic components in an electrical circuit; for example, to tailor a massproduced circuit to a particular application.

Whilst variable resistors and capacitors are widely used for this purpose a need remains for a similar method of varying higher value capacitance by means of readily releasably connecting, both mechanically and electrically, such components to a printed circuit board. The one or more discrete electronic components may be passive components in the form of ceramic disc or electrolytic capacitors, thus, realising a method for providing an effectively variable high value capacitance by interchanging such capacitors. The second electrical device may be a single component to achieve simplicity. The second electrical device may be two or more components to achieve a high degree of flexibility in forming a compound component.

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Suitable permanent magnets for use with the invention are magnets with surface magnetic flux of greater than 1,000 Gauss, more preferably greater than 2,000 Gauss and most preferably between 3,000 and 6,000 Gauss. Such magnets give sufficient magnetic adhesion to create an adequate mechanical securing force whilst also avoiding significant variation in electrical contact when used in devices of miniature and sub-

miniature size for use in electronics circuits. Such powerful magnets are advantageous in that they cannot, under normal circumstances, be forced into contact, such as would form an electrical contact as required by the this invention, if surfaces of the same polarity are made to approach. Magnets for the securing of a non-magnetically attractable component between, more particularly by sandwiching such a component between magnets,. are preferably of 3,000 surface Gauss or greater and are further preferably primarily attached not more than 6mm apart.

Permanent magnets for use in the invention preferably comprise neodymium iron boron magnets. A suitable grade, using industry notation, is N30 a preferred grade is N35H.

Such devices may be solid units of magnetised nickel-plated NdFeB made from compacted and sintered powder. A method of making such permanent magnets is to sinter a NdFeB nnagnet from a powder having a composition comprising 14 parts Iron, 2 parts Neodymium and 1 part Boron. The manufacturing process may comprise the steps of aligning unsintered particles in a Could, compacting, sistering and then metal plating the device so formed. Alternatively particles may be sintered, metal plated and then magnetised. Suitable metals for plating include, nickel, chromium and gold. Optionally the sintered articles may be machined. A plastic coating step may also be incorporated on surfaces not participating in electrical contact.

Permanent magnets for use in the invention may preferably be retained in a retaining means such as a metal cup and may further preferably have a lead attached either directly or to the retaining means. The retaining means may retain the magnet by being crimped about a magnet, by a close interference fit, by a resilient means, by adhesion, by soldering or other means known in the art. If soldering is used the magnet is preferably pre-coated with a solderable material, such as by gold plating, and is magnetised after heat treatment for effecting the electrical connection. Alternatively, as in for example, surface mounting a suitably coated magnet may be attached by a cold

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soldering mechanism such as ultrasonic welding. The method of the invention therefore may include the locating of surface mount electronic components upon magnets surface mounted on a printed circuit board.

Components thus mounted by magnetic attachment to magnets are securely mechanically and electrically connected whilst upon attachment and removal little or no mechanical distortion of parts occurs and, in particular little or no shearing action to potentially wear away a contact surface is present. The method and devices of the invention, using magnets, thereby provide for the releasable magnetic attachment of electrical components without requiring a mechanically interlocking component.

Connection of electrical components may be facilitated by the attachment of small steel plates, for example thin discs to act as electrical contact points and magnetically attractable attachment points for use with the present invention. The attachment of magnets to components may also be used particularly if components require attachment in a given orientation.

However, it is also within the scope of the invention to attach magnets to a first electrical device, by for example soldering, wherein the attachment is by means of a flexible wire such that magnetic attachment to second devices of variable geometry may be enabled by moving the magnet on one end of the wire to contact the second device whilst another end of the wire contacts a main body of the first device. Here a principal advantage of the invention is in the ability to obtain secure releasable electrical connection to electrical devices of varying size. A method of realising secure yet adjustable releasable connections to circuit boards is therefore achievable. The devices and method of the invention allows stresses from adjustments to fit varying sizes of devices and from inserting and removing connectors to be significantly decoupled from a circuit board by the use of a flexible elongate electrical connector between a magnet and circuit board. the elongate connector is preferably a single strand of wire rather than a flex. Stress cracking of printed circuit boards can thereby be significantly ameliorated.

Connection by a nnethod and devices according to the invention wherein a flexible coupling is used between a device, and a magnet attached to a device is particularly advantageous as electrical and mechanical connection of a magnet to a circuit board by soldering is facilitated as the risk of damaging the magnet by prolonged heating from a

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soldering process Is greatly reduced. This is particularly so when an end of an elongate flexible connector remote from an end attached to the magnet is soldered.

Also according to the invention there is a method of releasably attaching one or more discrete electronic components between two permanent magnets located on a printed circuit board. The components are preferably secured by an attractive magnetic force between said magnets more preferably by sandwiching said discrete components between said permanent magnets. The electrical component or components may comprise a magnetically attractable material, more preferably such a magnetically attractable material may be present as surfaces forming an electrical contact portion of the electronic component or components. Suitable components are pen cell type batteries. Particularly suitable components are electrolytic capacitors. Such components may, for example, be added in series to appropriately provide greater variation in available capacitance.

A method of conveniently adjusting the values of electronic components in an electrical circuit, for example, to tailor a mass produced circuit to a particular application can therefore be performed. In particular a method of varying high value capacitance by means of readily releasably connecting both mechanically and electrically capacitors to a printed circuit board can be realised.

Particularly, but not exclusively, when an electrical device, such as a first electrical device, for use with the invention is an electrical sub assembly, more preferably when that sub assembly is a printed circuit board all the magnetically attractable electrical contact points may be between pairs of permanent magnets. This has the advantage that incorrect magnetic attachment of circuit boards, when circuit boards comprise the first and second devices is avoided if the magnets and their polarities are arranged so as to stop incorrect assembly by means of magnetic repulsion. An electrical sub assembly comprises a set of interconnected electrical or electronic components.

In addition in electronics circuits there is often a requirement that many connectors are present. However, when many connectors are present it is necessary to utilise a plurality of connector types and connector pin configurations so as to ensure that incorrect connections are not made. However, this solution often requires a large

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number of different types and shapes of connectors in any given device. This adds complexity to a manufacturing process, to the associated components stocking process and to associated ordering processes and so forth, in electronic circuits' manufacture. It would be preferable that only one sort of connector be used, yet without the potential for any Disconnection, for example by the connectors themselves actively avoiding engagement with the wrong sort of connection. There is therefore a need for an electrical connector such that the electrical connector, whilst, mechanically the same as other connectors, may be otherwise modified so that it itself determines which electrical contacts it is capable of making and which contacts it is not capable of making with other connectors which are otherwise mechanically identical.

According to a second aspect of the invention there is provided a system for providing a self selecting connector for releasably establishing two or more electrical contacts between two electrical connectors wherein said connectors are electrically and mechanically connected by means of permanent magnets and wherein the self selection is provided by means of arranging the orientation of the permanent magnets such that only connectors with complementary arrangements of magnets are capable of securing electrical and magnetic connection by means of magnetic attraction between the permanent magnets. Hence, by choice of orientation of the polarity of said permanent magnets such connectors may be made to, or not made to electrically contact the other connector, i.e. the pattern of North or South of the exposed magnetic faces of the electrical connectors can be tailored to attach to magnets in a complementary connector and actively repel for an undesirable connection. The above system is particularly suitable for connecting printed circuit boards to one to another.

The system of the invention enables fewer different connector types to be used in an electrical assembly, enables the risk of Disconnecting connectors to be greatly reduced as incorrect connections are actively repelled by strong magnets of like polarity and correct connections from magnets of dissimilar polarity form strong electrical and mechanical connections. The connectors thereby effectively self-select which other connectors they are suitable for connection with.

In most applications of the invention the use of high strength magnets gives rise to very powerful repulsive forces between connectors of incorrect polarity, thus stopping

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meaningful electrical contact being made. However, where high voltages are involved the potential for arcing between magnets on close approach may be present. In addition where multiple pole connectors, as in the second aspect of the invention, are used a net attraction between an aggregate of connectors may result and individual contacts may thereby be forced. Particularly, but not exclusively, in the above situations a further embodiment of the invention may be used. Electrically contacting, mechanically securing magnets may be movably located in an insulating housing such that the magnets may move in a housing to approach one another and contact if the faces of the magnets are of opposite polarity and if of like polarity may retreat into the housing to avoid a spark-

gap forming or other contact being made. The magnets may be resiliently biased within the housing.

According to a third aspect of the invention there is provided an electrical component for the attachment of other magnetically attractable electrical components, comprising a permanent magnet secured in an electrically contacting electrically conductive mechanical holding means to which means a flexible elongate electrical contact and attachment means is electrically and mechanically attached by magnetic attraction at one end to the electrically contacting electrically conductive mechanical holding means and at the remote end is solderable to a conventional printed circuit board. The flexible elongate electrical contact may be in the form of a wire or metal braiding.

An electrical component for use in the invention and in method of the invention as described above may comprise a component for modifying an electric current forms the sole electrical connection between the permanent magnet and the holding means and the elongate electrical connector is not in direct electrical contact with the permanent magnet. Suitable components are as described above under discrete devices. A preferable component is a diode, such a device, when used as a battery connector can act to stop current flowing if a battery is incorrectly connected.

The method, devices and system of the invention are particularly advantageous in that Optimum electrical contact is obtained as magnets, which form the electrical contact surface in the invention, automatically orientate themselves to give the greatest available surface contact by means of their magnetic attraction.

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The method and devices of the invention may be used to form a modular educational system for teaching electronics, comprising a matrix of magnetic connectors between which electronics components can be located as hereinbefore described.

Examples of the invention will now be described by way of illustration only, with reference to the accompanying drawings, in which: Figure 1 shows a device of a first embodiment of the invention, in side elevation, as a cross section; Figure 2 shows an end elevation of the device shown in Figure 1; Figure 3 shows a second embodiment of the invention, in side elevation, as a cross section; Figure 4 shows devices of the invention in association with a battery; Figure shows a side elevation in cross section of devices of the invention when used in conjunction with modular electronic components; Figure 6 shows devices of the invention, in side elevation in cross section, connecting printed circuit boards; Figure 7 shows devices of the invention, in side elevation in cross section, resisting connection of two printed circuit boards; Figure 8 shows an end elevation of a connector of a third embodiment of the invention; Figure 9 shows a side elevation in cross section of a fourth embodiment of theinvention; Figure 10 shows a side elevation in cross section of devices of the fourth embodiment of the invention connected;

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Figure 11 shows a side elevation in cross section of devices of the fourth embodiment of the invention resisting connection and; Figure 12 which shows a side elevation in cross section of a device of a fifth embodiment of the invention.

In the drawings the same or similar features are denoted by common reference numerals. Figures 1 and 2 show a first embodiment of the invention 2. A permanent magnet 4 is retained by a push fit in a holder 6 comprising rear face 8 and side wall 12, which are in electrical contact with magnet 4. Holding means 6 also comprises an electrical contact wire 10, which is a tinned copper wire. Magnet 4 comprises a nickel-plated neodymium iron boron magnet of cylindrical form and holder 6 comprises a thin tinned copper shell, which may alternatively be crimped on magnet 4 to hold magnet 4 in place.

Figure 3 shows a device of a second embodiment of the invention 20. Device 20 comprises a device of the first embodiment of the invention 2 with additional plastic sheathing 22. The plastic sheathing 22 extends over the end of the device to effectively recess the electrically contactable portions of the end of the device. Plastic sheathing 22 is attached by heat shrinking a polymeric material over the surface of device 2.

Figures 4 to 7 show applications of devices of the invention, in particular device 2 of the first embodiment of the invention.

Figure 4 shows two devices of the invention 2, attached to a printed circuit board 30 by solder joints 32, which attach lead wires 34 of devices 2 to a copper track (not shown) on circuit board 30. Devices of the invention 2 are located such that a conventional battery 36 comprising magnetically attractable end components 38 may be placed between magnetic faces of magnets 4 of devices of the invention 2. Devices of the invention 2 hold battery 36 in place by magnetic attraction and also give electrical contact to the end faces 38 of the battery by electrical contact with magnets 4. Thus a method of retaining a battery in electrical contact on a circuit board is disclosed.

P2 l 640GB-4 Figure 5 shows devices of the invention 2 attached to a circuit board 30 by solder joints 32. Solder joints 32 are part of the printed circuit of the circuit board 30 via copper tracks thereon (not shown). In between devices of the invention 2 are retained modular elements 40 and 42. Modular element 40 is a resistive element comprising magnetically attractable faces 44, which serve as an electrical contact between the surfaces of resistive device 40 and the resistive composition 46 in the modular device. A capacitive element 42 is also present and this similarly comprises magnetically attractable electrically connectable faces enclosing a capacitive structure 48.

In use, as shown in figure 5, devices of the invention 2 may have placed between them a number of different modular elements comprising resistive elements, capacitive elements, inductive elements, conductive spacer elements and so forth, in a manner such that a given resistance, capacitance or inductance may be suitably built up by inserting modular elements between devices of the invention 2, such that the elements of the invention 2 are retained in physical contact and mechanical support, by magnetic attraction and in electrical contact, by electrical contact with opposite faces of the elements, of the various units. The magnetic attraction and electrical contact may be indirect, as when a modular element is sandwiched between other modular elements.

Variations include where a modular element 40 is not magnetically attractable but is retained by the mutual attraction of the magnetic members 4.

Figures 6 and 7 show a further application of the invention. Devices of the invention 50, 52 comprise magnets 4 as previously described. In device of the invention 50, magnet 4 is orientated with a North pole away from the base of the retaining holder. Device 52 of the invention has magnet 4 orientated with the South pole away from the base of the retaining holder. Devices of the invention 50 and 52 are connected to circuit boards 56 and 58 by means of solder connections 54 and 60. By placing devices of the invention 50 and 52 in proximity devices of the invention are attracted one to another and a mechanical and electrical contact is formed in the junction between the two devices 62, such that the circuit boards are held in physical and electrical contact. Figure 7 shows the effect of bringing in close proximity devices of the invention 50 with fields orientated

in a like manner, such that circuit boards 56 and 58 are no longer able to be brought into mechanical and electrical contact using reasonable force due to repulsion, as illustrated by the double headed arrow on the diagram.

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Figure 8 shows a third embodiment of the invention. This is an end view of a modified conventional D-type connector, comprising a number of contacts 72 surrounded by an earth shield 74. Such a connector can be connected to a like connector simply by offering up the two faces one to another whereupon magnetic attraction holds the devices in physical and electrical contact. Of particular note is the potential for the arrangement of the magnetic field polarity associated with adjacent magnetic elements

72', 72", 72'' and so forth. By suitably orientating the magnetic fields of these individual

units it is possible to make a template which is only magnetically recognizable (by magnetic attraction), by a similar template of another such device, such that a very large multiplicity of connectors may be present in a given device whereby a user is prevented from misconnecting connectors, even though the connectors may otherwise look and appear the same. In such a device care is taken to make sure that combinations of dissimilar magnetic patterns of adjoining elements are not present which are capable of still having a net magnetic attraction.

Figures 9, 10 and 11 show a fourth embodiment of the invention 80. Magnet 4 is located in electrically insulating housing 82 in which it is slideably movable between opening 86 and further into recess 88. Magnet 4 is fixed to, resiliently biassed by and in electrical contact with coil spring 84 which is itself at a remote end fixed to and in electrical contact with electrically conducting end plate 8. End plate 8 is connected to lead 10 for connection into, for example, the body of a connector of the third embodiment or to a printed circuit board (not shown). Use of the fourth embodiment of the invention with the third embodiment of the invention overcomes the stated need for care to be taken in the combinations of magnetic fields.

In use (Figures 10 and 11) close approach of devices of the fourth embodiment wherein the magnetic faces 90 of the magnets 4 are of opposite polarity draws magnets 4 together to form an electrical contact across the faces 90 of the magnets. Close approach of devices of the fourth embodiment wherein the magnetic faces 90 of the magnets 4 are of like polarity leads to magnets 4 retreating into cavity 88 as spring 84 is compressed. Therefore even if the ends 92 of insulating housing 82 are brought into physical contact no electrical contact between the surfaces 90 of magnets 4 occurs.

P2 l 640GB-4 Therefore the potential for sparking across the gap 94 between electrically connected surfaces 90 of magnets 4 is reduced.

Figure 12 shows a fifth embodiment of the invention. A permanent magnet 4 is retained in a holder 100 comprising rear face 8 which is in electrical contact with electrical contact wire 10 and resistor 102 but not in electrical contact with holder 100 side wall 12. Magnet 4 comprises a nickel-plated neodymium iron boron magnet of cylindrical form, the rear face 104 of which is in electrical contact with resistor 102 but not tubular side wall 12.

Alternative components to resistor 12 may be used such as a diode, capacitor or other discrete electronics component.

The terms magnetic adhesion and magnetic attachment refer to an attachment that is due to the force of magnetism leading to adhesion or attachment. The word attachment when not prefixed by the word magnetic is generally used to denote attachment in the normal meaning of the word. A device of the invention may be magnetically attached to another device (i. e. a releasable magnetic attachment) whilst itself be attached to and forming part of a device (e.g. by being soldered to it). Physical attachment by magnetic attachment denotes the physical component resulting from a releasable magnetic attachment, usually present here alongside an electrical attachment.

Claims

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1. A method of forming a releasable electrical connection, the method comprising the steps of: providing a first electrical device and a second electrical device; said first and second electrical devices being connected by at least one permanent magnet so as to form a releasable electrical connection therebetween.

2. A method according to claim 1 wherein the electrical connection forms part of an electrical circuit.

3 A method of forming a releasable electrical connection according to either claim 1 or claim 2 by providing that the first or second electrical device is held between two or more permanent magnets so as to form a part of an electrical circuit.

4. A method according to any one previous claim wherein each of the at least one permanent magnet is attached to either the first or second device.

5. A method according to any one of claims 1 to 4 wherein the electrical devices are releasably electrically connected by magnetic attachment.

6. A method according to claim 5 wherein the electrical devices are releasably electrically connected only by magnetic attachment.

7. A method according to either of claims 5 or 6 wherein a permanent magnet on the first device directly physically and electrically contacts a permanent magnet on the second device by means of magnetic attraction to form the releasable electrical connection.

8. A method according to any one previous claim wherein the first or second electrical device comprises a printed circuit board.

9. A method according to any one previous claim wherein the first and second electrical devices comprise printed circuit boards.

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10. A method according to any one previous claim wherein the first or second device comprises one or more discrete electronic components.

11. A method according to any one of claims 1 to 8 wherein the first or second device consists of one or more discrete electronic components.

12. A method according to either claim 10 or claim 11 wherein the one or more discrete electronic components are releasably magnetically attached by means of an attractive magnetic force between two or more of the permanent magnets.

13. A method according to claim 12 wherein the attractive magnetic force between two or more of the permanent magnets acts to sandwich the one or more components between said permanent magnets.

14. A method according to claims 13 wherein the one or more discrete electronic components comprise passive electronics components.

15. A method according to claim 14 wherein the one or more discrete electronic components comprise a component of consumable characteristics.

16. A method according to claim 14 wherein the one or more discrete electronic components comprise a capacitor.

17. A method according to any one of claims 10 to 16 wherein the first or second device comprises a plurality of discrete electronic components.

18. A method according to any one of claims 10 to 16 wherein the first or second device consists of a plurality of discrete electronic components.

19. A method according any one of claims 1 to 12 wherein all releasable electrical connections between the first and second electrical devices consist of contacting pairs of permanent magnets.

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20. A method according to any one previous claim wherein the permanent magnets are magnets with surface magnetic flux of greater than 1,000 Gauss.

21. A method according to claim 20 wherein the surface magnetic flux is between 3,000 and 6,000 Gauss.

22. A method according either of claims 20 or 21 wherein the permanent magnets comprise neodymium iron boron magnets.

23. An electrical component for use in the method of claim 1 comprising a permanent magnet, a holding means for the magnet and an elongate electrical connector means for connecting to a printed circuit board wherein the magnet is exposed on one face for the purpose of establishing an electrical contact to a device to which it can be releasably magnetically secured.

24. An electrical component according to claim 23 wherein the flexible elongate electrical contact is in the form of a single strand of wire.

25. An electrical component as described in either claim 23 or 24 wherein an electronics component for modifying an electric current forms the sole electrical connection between the permanent magnet and the holding means and the elongate electrical connector is not in direct electrical contact with the permanent magnet.

26. A system for providing a self selecting connector for releasably establishing two or more electrical contacts between two such electrical connectors wherein said connectors are electrically and physically connected by means of permanent magnets and wherein the self selection is provided by means of arranging the orientation of the permanent magnets such that only connectors with complementary arrangements of magnets are capable of securing electrical and magnetic connection by means of magnetic attraction between the permanent magnets.

27. A method of releasably connecting printed circuit boards as hereinbefore described with reference to the accompanying description and Figures 6 and 7 of the drawings.

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28. A method of releasably connecting electronics components as hereinbefore described with reference to Figure 5 of the drawings.

29. An electrical connector for holding an electrical device by magnetic attraction as hereinbefore described with reference to the accompanying description and Figures

1 to 3; or Figure 8 of the drawings.