Circuit continuity tester and method

[0002] This application is a continuation-in-part of Ser. No. 08,935,154 filed Sep. 22, 1997 now abandoned.

[0003] The present invention relates to means of testing continuity of an electrical circuit and, more specifically, to apparatus for adapting a conventional flashlight for use as a continuity tester.

[0004] In many electrical applications, it is sometimes necessary or desirable to have a quick and easy means for testing circuit continuity, i.e., for determining whether there is an electrical path for current flow between two points. Many devices have been provided in the prior art for performing this function. Among such devices are those which include an incandescent bulb or other light-emitting means for providing a visual indication of presence or absence of circuit continuity in the apparatus or line under test. Often, the continuity tester includes a pair of wires terminating in alligator clips for attachment at the points between which continuity is to be tested. The prior art also includes means for modifying conventional flashlights to permit their use as circuit continuity testers.

[0005] The principal object of the present invention is to provide novel and improved means for adapting a conventional flashlight to act as a circuit continuity tester.

[0006] The apparatus of the invention is used in conjunction with a conventional hand-held flashlight, preferably of compact construction, having a detachable metal clip by which it may be attached to a pocket or other part of the clothing. The flashlight includes the usual hollow body portion wherein the battery or batteries are mounted. Upper and lower end caps are threaded to opposite ends of the body, the bulb being mounted in the upper end in conductive relation with the positive battery terminal. An electrically conducting spring is urged by the lower end cap, when the latter is fully engaged with the body, into conductive contact with the negative side of the batteries. Both end caps and the body, as well as the spring, are of conductive material and thus in electrical connection with the negative side of the batteries. An on-off switch is provided to selectively make or break the circuit connecting the bulb to the negative terminal of the batteries.

[0007] According to the present invention, an insulated electrical wire passes through an opening provided for such purpose in the lower end cap, placing one end of the wire inside and the other end outside the flashlight body. The end inside the body is soldered to an electrically conductive member, e.g., a rivet or a metal washer of appropriate size, and the end outside the body is soldered to the metal pocket clip which may be selectively placed in or removed from encircling relation to the flashlight body. The plate to which the inner end of the wire is soldered is placed between the spring and the negative side of the battery, being urged into conductive contact with the battery by the spring. In a first disclosed embodiment, a layer of insulating material is interposed between the metal plate and the spring, preferably by being coated upon or otherwise affixed to the surface of the plate opposing the spring. In a second disclosed embodiment, the normal flashlight spring is removed and replaced by a layer of somewhat resilient electrically insulating material which is compressed between the end cap and negative battery terminal; the head of a rivet is urged by the resilient layer into engagement with the negative battery terminal and the stem of the rivet extends into a through opening in the resilient layer where it contacts the end of the wire inside the flashlight body.

[0008] Thus, with the flashlight switch in the “on” position, the bulb is illuminated only when the metal pocket clip and metal exterior of the flashlight, i.e., the end caps or body, are placed in contact with two points between which electrical continuity exists. In this manner, the modified flashlight may be employed to test for circuit continuity between two points simply by placing the pocket clip in contact with one point and any other exterior surface in contact with the other point and observing whether or not the bulb illuminates.

[0009] The foregoing and other features of construction and operation of the invention will be more readily understood and fully appreciated from the following detailed description, taken in conjunction with the accompanying drawing.

[0010] FIG. 1 is an exploded, perspective view of a flashlight modified for use in the present invention;

[0011] FIG. 2 is an elevational view, in full section, of the flashlight of FIG. 1;

[0012] FIG. 3 is a schematic illustration of the operation of the invention;

[0013] FIG. 4 is an elevational view of an alternate embodiment of apparatus for modification of the flashlight of FIGS. 1 and 2; and

[0014] FIG. 5 is a fragmentary, enlarged, elevational view of portions of the apparatus of FIG. 4.

[0015] Referring now to FIGS. 1 and 2, a flashlight modified in accordance with the teachings of the present invention is denoted generally by reference numeral 10. Flashlight 10 is preferably of somewhat compact construction, an example of a commercially available product suitable for modification to the construction of the circuit tester of the present invention being that sold under the trademark Mini-Maglite by MAG Instrument, having an axial length of about six inches. The conventional portions of flashlight 10 include hollow, cylindrical body member 12, having what are termed upper and lower ends 14 and 16, respectively, upper end cap 18, bulb 20, lower end cap 22, coil spring 24 and metal pocket clip 26. Body member upper end 14 is externally threaded to engage upper end cap 18, and lower end 16 is internally threaded to engage lower end cap 22. Bulb 20 is powered by a pair of AA-size batteries 28aand 28bwhich are mounted in series within body member 12.

[0016] As best seen in FIG. 2, upper end cap 18 includes two threadedly connected portions, 18aand 18b.Portion 18acarries the usual reflector 32 and lens 34, access to which is provided by removal of portion 18b.A pair of leads extend from bulb 20 through openings in circular plate 36, which is rotatably carried in upper end 14 of body member 12. Plate 36 is engaged by opposing surfaces of fins 38 on reflector 32 (providing on-off switch). Spring 24 is installed between lower end cap 22 and the lower end of battery 28b.In the conventional, unmodified form of flashlight 10, when end caps 18 and 20 are fully engaged with the upper and lower ends of body member 12, spring 24 is compressed between lower end cap 22 and battery 28b,being in conductive contact with the negative terminal thereof. The positive terminal of battery 28bis urged into contact with the negative terminal of battery 28a,and the positive terminal of the latter is positioned for contact with the leads of bulb 20.

[0017] All parts thus far described are present in a commercially available, unmodified flashlight. Modification thereof to provide the circuit continuity tester of the present invention involves drilling a hole 43 through lower end cap 22 and inserting therethrough insulated wire 40 whereby, when end cap 22 is engaged with lower end 16 of body 12, one end of wire 40 is inside and the other end outside the body. A bare portion (i.e., with insulation removed) of the end of wire 40 outside the flashlight body is soldered or otherwise connected to clip 26, and the end inside the body is connected to conducting plate 42, e.g., a metal washer. When the parts are assembled, one side of plate 42 is urged by spring 24 into conductive contact with the negative side of battery 28b.The other side of plate 42 is coated with a layer of plastic or other non-conductive material 44. Thus, spring 24, and consequently lower end cap 22, body 12 and upper end cap 18, are not in conductive contact with the negative side of battery 28b.

[0018] The modified flashlight 10 may now be used to test for circuit continuity between two points. For example, the schematic diagram of FIG. 3 indicates an electrical path 46 between points A and B. Metal pocket clip 26 is detached from body 12, and the on-off switch is placed in the “on” position. Bulb 20 does not illuminate since it is not in electrical communication with the negative side of the batteries. However, such communication is provided when clip 26 is placed in contact with point A, and any part of the metal exterior of the flashlight (body 10, upper end cap 18 or lower end cap 22) is placed in contact with point B. Illumination of bulb 20 indicates circuit continuity between points A and B; conversely, non-illumination indicates an interruption, or non-continuity, of a conducting path between points A and B.

[0019] An alternate version of apparatus for adapting a conventional flashlight to use as a circuit continuity tester is shown in FIGS. 4 and 5. Rather than drilling a passageway through the lower end cap which is part of the conventional flashlight, the end cap and the conventional coil spring are removed and replaced by the apparatus of this version which, in most applications, will be preferred over the first disclosed version. End cap 22 is replaced by unitary member 50, of electrically conducting material, having cylindrical portions 52 and 54 of essentially the same diameter as flashlight body 12 and separated by first smaller diameter portion 56. Externally threaded portion 58, separated from portion 54 by second smaller diameter portion 60, mates with the internal threads at lower end 16 of body 12. Internal cavity 62 extends through portions 58, 60, 54 and 56, and through opening 64 communicates with cavity 62 through portion 56.

[0020] Wire 40′ extends through the passageway provided by internal cavity 62 and opening 64. The bare end portion of the wire remote from member 50 is electrically connected to clip 26, as in the previously described version. Cylindrical bushing 66 of somewhat resilient, electrically insulating material has a central opening and a diameter substantially equal to that of threaded portion 58. An electrically conducting rivet 67 includes head 68 and stem 70 which extends into the central opening of bushing 66. Bare end 41 of wire 40′ is electrically connected to rivet 67 by soldering and/or being inserted in the hollow interior of stem 70 and crimping the stem, or by other means. When portion 58 is fully engaged with lower end 16 of flashlight body 12, bushing 66 is compressed between the end of section 58 and the lower end of battery 28b.Rivet head 68 is urged into electrical engagement with the negative terminal of battery 28b,thereby placing clip 26 in communication, through wire 40, with the negative side of the batteries.

[0021] As a further refinement, enlarged portion 72 is preferably affixed to wire 40′, as shown in FIG. 5. Portion 72 may be a conical piece of insulation with a maximum diameter greater than that of opening 64, or may simply be a knot in wire 40′. In any event, portion 72 is so positioned that it prevents an outwardly pulling force on wire 40′ from being applied to the portion of the wire within cavity 62, tending to pull rivet head 68 away from the negative terminal of battery 28b,and/or disturbing the connection between wire end 41 and rivet 67. Providing engagement portion 72 with a conical configuration offers the added advantage of its acting as a seal, effectively preventing entry of moisture and foreign matter into internal cavity 62.

[0022] Operation of the modified flashlight as a circuit tester is the same in both disclosed versions. The probe, represented in the disclosed versions as a pocket clip, is placed in contact with one of the points between which continuity is to be tested and any other exterior portion of the flashlight (upper or lower end cap or body) is placed in contact with the other point. With the conventional switch in the “on” or closed position, the bulb will illuminate only if the circuit between the negative battery terminal and the bulb contact is completed by circuit continuity between the two points. Thus, the invention involves breaking the usual circuit continuity between the negative battery terminal and one side of the on-off switch in a conventional flashlight and providing a probe (clip) to complete the circuit. It should be noted that the probe will complete the circuit between the switch and negative battery terminal by being in electrical contact with the flashlight body, thereby permitting normal use of the flashlight through the on-off switch, as well as when detached from the body and used in circuit continuity testing. Any excess length of wire 40′ outside the flashlight body may be neatly wrapped around reduced diameter portion 56 of member 50 when clip 26 is affixed to body 12.