Abstract:
A circuit testing device includes a handle with a hollow interior, a conductive probe projecting from one end and a removable cap with a wire and clamp projecting from the opposite end A subassembly retained within a counterbore in the handle includes a polarity sensitive buzzer and light in a parallel circuit configuration whereby the device is useful for determining polarity, circuit continuity, and battery drain.

Description:
BACKGROUND OF THE INVENTION 
     In a principal aspect the present invention relates to a device for testing electric circuits, and more particularly, a hand held circuit testing device which includes various attachments that interact with leads and contacts and wherein the circuit testing device provides a visual, as well as an audio indication of a closed circuit, a polarity, short circuit and battery drain test. 
     Modem vehicles often include a wide variety of electrical items all powered by a direct current battery. Such items are typically incorporated in low voltage circuits, e.g. 28 volts or less. Often, the wiring in a vehicle is difficult to access and since there may be multiple electrically driven components, circuit checking and circuit testing with respect to each of those multiple components and items is time consuming and complex. Thus, troubleshooting the electrical system of a motor vehicle is often a particularly challenging task. 
     Consequently, there has developed a need for a device which will enable and facilitate easy testing of circuits in such an environment. Such testing includes the need to identify short circuits, to check circuits from a distance, to check polarity, to check battery drain, and to check whether the circuit is a complete and closed circuit. Often, attempting to check such circuits using a device which operates a light in response to a low voltage current flow is inadequate for diagnostic and vehicle repair situations. Audio responses are often required inasmuch as the light may not be visible to the mechanic. In sum, there has developed an important need for a compact, portable, low voltage circuit testing device or kit. 
     SUMMARY OF THE INVENTION 
     Briefly, the present invention relates to a circuit testing device which provides both audio and visual indication of a direct current voltage. Te device is in the form, shape and size of a typical heavy duty screwdriver with lead wires and probes project from the opposite ends of the device for connection to wires and contacts associated with a circuit to be tested. Thus, the device includes a hollow handle with an audio buzzer and light subassembly slidably mounted in the handle and with lead probes and/or wires projecting from the opposite ends of the handle electrically connected to the subassembly. When a closed circuit is sensed, a buzzer, as well as a light, provides indication of voltage. The buzzer is, preferably, polarity sensitive in order to give the user of the tool or device additional flexibility when diagnosing and servicing low voltage electric circuits typically as incorporated in motor vehicles. It is noted, however, tat the circuit testing device, or kit, may be used in any environment where low voltage testing is appropriate and thus, the use of the device is not limited to the automotive or vehicle repair field. The audio buzzer and the electric light are retained within a translucent handle. They are mounted on a transportable bracket and are maintained in parallel electric array in the test circuit. 
     Thus, it is an object of the invention to provide a circuit testing device which works in and for circuits having a low voltage wherein the device can be used to perform multiple functions including detection of a short circuit, detection of circuit continuity remotely by a sound indicator, detection of polarity in a circuit, and investigation and determination of battery drain. 
     It is a further object of the invention to provide an easily manipulated circuit testing device which is manually operated and which includes various attachments to facilitate the test protocol desired by the user. 
     Another object of the invention is to provide a rugged and dependable circuit testing device which may be assembled and disassembled easily to permit ease of repair and replacement of parts. 
     Yet another object of the invention is to provide a circuit testing device which is not costly. 
     These and other objects, advantages and features of the invention will be set forth in the detailed description which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the detailed description which follows, reference will be made to the drawing comprised of the following figures: 
     FIG. 1 is a plan view of the circuit testing device in accord with the invention including depiction of an optional clip and a wire retention probe; 
     FIG. 1A is an enlarged, partial cross sectional plan view of the handle of the circuit tester; 
     FIG. 2 is an exploded isometric view of the device of FIG. 1; 
     FIG. 3 is an isometric view illustrating use of the circuit testing device to investigate battery drain; and 
     FIG. 4 is an isometric view of the use of the circuit testing device to investigate polarity. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the figures, the circuit testing device of the invention includes a handle  10  having the form of a typical screwdriver handle. The handle  10  is generally hollow and includes a uniform diameter counterbore  12  which is accessible from one end of the handle  10  through a threaded opening  14 . The counterbore  12  is centered axially within the handle  10  and extends from the opening or end  14  substantially through the handle  10  toward the opposite end  15 . Intermediate the ends  14 ,  15  of the handle  10  is a passage  18  through a side wall leading to the counterbore  12 . Passage  18  allows sound from a buzzer (described below) to be emitted from the counterbore  12  in the handle  10  so that it may be heard by a user of the circuit testing device. Typically, the handle  10  is made from a translucent or transparent molded plastic material. 
     The open end  14  of the handle  10  is adapted to receive a cap  20  which includes a threaded projection  22  that screws into the open end  14  of the handle  10 . An axial counterbore  24  in cap  20  extends inwardly into the cap  20 , and a contact  26  is provided at the inside or interior end of the counterbore  24 . A lead wire  28  with an end clamp  30  extends from the cap  20  and is connected to the contact  26 . The contact  26 , lead wire  28  and clamp  30  may thus form part of an electric, low voltage d.c. circuit. 
     At the opposite end of the handle  10 , a metallic, electrically conductive metal probe  32  extends axially. The probe  32  includes an inner contact, or first contact,  34  on the inside of the counterbore  12 . The probe  32  extends axially from the contact  34  through the end  15  of the handle  10  and terminates with a point  36 . Reduced diameter section  38  is provided on the probe  32  adjacent point  36  at end  37  for cooperation with a telescoping fitting  50  described in greater detail below. 
     The end or section  37  of the probe  32  is adapted to slidably receive an alligator clip contact  40 . The alligator clip  40  may be used to provide electrical contact through the probe  32  to the interior of the handle  10 , namely, to the counterbore  12 , and more particularly to a sensor subassembly  70  (described below). When clip  40  is removed, the point  36  may be used to engage with a wire or contact and thereby provide an electrical circuit to the interior counterbore  12  of the handle  10 . 
     A telescoping, slidably insertable fitting  50 , typically made from a plastic, nonconductive material, includes an end hook  52  which is axially aligned with the point  36 . More particularly, a passage  54  in the hook  52  is aligned with the point  36 . The fitting  50  includes an axial bore or throughpassage  56  with an internal rib  58 . The throughpassage  56  has a shape and diameter which enables mounting the fitting  50  telescopically on the probe  32 . The reduced diameter section  38  of the probe  32  results in an annular flange  39  which in combination with the flexible, internal rib  58  serve to retain the fitting  50  on the probe  32 . The fitting  50  is thus retained on the reduced diameter section  38  by the rib  58  which impinges against flange  39  to limit axial travel of fitting  50 . 
     A circumferential radially extending flange  60  of fitting  50  provides a dual function. That is, a spring  62  interposed between the end  15  of the handle  10  and flange  60  biases the fitting  50  away from the handle  10  toward engagement with flange  39  of probe  32 . The flange  60  may be manually gripped to counteract the spring force of spring  62  thereby axially telescoping the fitting  50  and thus moving the hook  52  toward engagement with point  36  to hold or retain an insulated wire by means of the hook  52  against the probe  36 . This action also permits the probe  36  to pierce the insulation on the wire held by hook  52  and thereby provide an electrical circuit. 
     An important feature of the invention is the sensor subassembly  70  which slides into the counterbore  12 . The sensor subassembly  70  comprises bulb socket  82  joined with a conductive mounting bracket  72 . Bracket  72  includes an upwardly depending bracket arm  74  for engagement with the probe contact  34 . A polarity sensitive buzzer  76  is mounted on the bracket  72 . The bracket  72  is soldered to an inside solder contact  106 . The inside solder contact  106  connects to spring loaded center contact pin  94  in bulb socket  82 . The bulb socket  82  receives a light bulb  84  which includes a pin  86  that mechanically engages with a retention slot  88  in the socket  82 . The outer shell of the bulb  84  is thus mechanically and electrically connected to the bulb socket  82  by a pin  86 . A center contact  90  of the bulb  84  engages with the conductive contact pin  94  biased by a spring  96  into engagement with the contact  90 . The contact pin  94  is in electrical contact with an inside solder contact  106  thus providing a circuit connection. 
     Bulb  84  includes a snap ring  98 , and a biasing spring  100  is positioned over the snap ring  98  to provide an electrical connection as well as a mechanical connection between the snap ring  98 , bulb base  110  and the contact  26  within the counterbore  24 . Thus, the spring  100  provides electrical as well as mechanical contact. The spring  100  also biases the entire subassembly  70  into the counterbore  12  and insures that positive electrical contact will be maintained between contact  34 , bracket  72 , and also between center light contact  26 , and bulb socket  82 . 
     The buzzer  76  includes a first lead  102  connected through outside solder contact  108  to bulb socket  82  and a second lead  104  which is connected to the inside solder contact  106 , bracket  72  and contact  94 . In this manner, the buzzer  76  is provided in parallel circuitry with the bulb  84 . 
     The inside contact  106  comprises a bracket, is mechanically and electrically attached to bracket  72 , and is mechanically attached to bulb socket  82  by means of an insulating member  85 . A rivet  87  with a through passage  89  retains the contact  106  outside contact  108 , socket  82  and insulator  85  joined together. The contact  94  is telescopically mounted in passage  89 . 
     The buzzer  76  is preferably a polarity sensitive buzzer which provides sound only when the leads are connected in a manner wherein the clamp  30  is attached to a negative contact. In such a circumstance, the probe  32  will be connected to a positive contact. Reversal of the polarity of contacts will not result in any buzzer sound even though the bulb  84  may be illuminated. The buzzer  76  thus provides a polarity responsive audio sound. 
     FIGS. 3 and 4 illustrate various modes of operation of the circuit tester. FIG. 3 illustrates an arrangement to check whether a battery is being drained. The protocol followed requires that the ignition and all switches in the vehicle are in the off position. The negative battery cable would then be removed. The ground clip or clamp  30  is then connected to the negative battery post and the probe  32  is attached to the negative battery cable. If the light and buzzer activate, then the vehicle is drawing 200 milliamps or more. That will indicate, of course, a battery drain situation. 
     FIG. 4 illustrates the use of the testing device to check polarity. In such a circumstance, the clamp  30  is attached to ground and the probe  32  to a wire. If the light  84  and buzzer  76  both are activated, the probe is connected to a positive contact. If the light  84  only activates, then the probe  32  is contacted to a negative pole or contact. 
     There are many other uses of the testing kit as described. The subassembly  70  construction, for example, may be varied without departing from the spirit, scope and functionality of the invention. The invention is, therefore, to be limited only by the following claims and equivalents thereof.