Abstract:
A battery tester determines a remaining level of charge of a battery mounted within a separate electronic device having an audio jack. The battery tester includes a plug and a circuit having a high impedance input amplifier. At least one electrical contact of the plug is electrically coupled to an input of the high impedance input amplifier. The plug is removably insertable within the audio jack such that the battery of the separate electronic device is electrically connected to the input of the high impedance input amplifier. When electrically coupled to the battery, an output of the high impedance input amplifier provides a signal proportional to the remaining level of charge of the battery, whereby the remaining level of charge of the battery is obtainable by the battery tester without having to remove the battery from the electronic device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a battery tester for determining the charge level of batteries, and more specifically, the present invention relates to testing the remaining charge level of batteries that are operatively mounted within closed battery compartments of musical instrument bodies and like apparatus without having to remove or disassemble access panels and the like and without having to physically remove the batteries from the battery compartments. 
         [0002]    As an example, electric guitars, bass guitars and other electric musical instruments typically have on-board tone control circuits that are battery powered, for instance, by one or two nine volt disposable or rechargeable batteries. The batteries are typically mounted within a battery compartment concealed within the instrument body and are accessible only by removing an access panel or the like fastened to the body with screws or like mechanical fasteners. Accordingly, if new batteries are needed or the existing batteries are to be tested, the access panel must be removed to expose and gain access to the old batteries and/or to replace the batteries. 
         [0003]    Most electric guitars, bass guitars and other electric instruments do not have built in battery charge measurement systems. With respect to such musical instruments, this creates a problem in that, if a performer begins to play an instrument and the remaining battery charge is weak, the sound quality of the instrument will degrade rapidly with little or no advance notice. Thus, existing batteries should be replaced with new batteries or removed, tested, and reinserted before any performance. 
         [0004]    Merely for purpose of example, battery testing devices and other portable testing devices are disclosed in general, for instance, by U.S. Pat. Nos. 3,974,441 issued to Van Den Haak; 5,003,250 issued to Hukuba; 5,376,887 issued to Saubolle; 5,216,371 issued to Nagai; 4,020,243 issued to Oldford; 6,121,753 issued to Walker et al.; 3,493,863 issued to Girdwood; 4,514,695 issued to Lau; 4,360,780 issued to Skutch, Jr.; 4,439,736 issued to Schwartz; D.330,519 issued to Wang; 1,337,160 issued to Riebeth; 4,743,831 issued to Young; 6,347,958 B1 issued to Tsai; and 4,533,864 issued to Austin. In particular, the &#39;441 patent to Van Den Haak discloses a device for checking the energy level of a battery in a powered model airplane, boat or car. This battery checking device includes a plug that is removably connectable to a battery recharging receptacle on the model airplane, boat or car and does not require the battery to be removed from the model to perform a check of the battery. 
         [0005]    While the battery testing and other devices disclosed by the above referenced patents may function in an acceptable manner, there is a need for a convenient and simple manner of testing battery charge level remaining in batteries installed within various electronic devices, such as musical instruments. Preferably, the battery check should be obtained without the need for fastener removing tools, such as screw drivers or the like, without the need to remove or disassemble access panels or the like, and without the need to gain direct access to, and/or remove, the batteries that are to be checked. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention is directed to a battery tester that can be used to determine a remaining level of charge of a battery mounted within a separate electronic device having an audio jack. The battery tester includes a plug and a circuit having a high impedance input amplifier. At least one electrical contact of the plug is electrically coupled to an input of the high impedance input amplifier. The plug is removably insertable within the audio jack such that the battery of the separate electronic device is electrically connected to the input of the high impedance input amplifier. When electrically coupled to the battery, an output of the high impedance input amplifier provides a signal proportional to the remaining level of charge of the battery, whereby the remaining level of charge of the battery is obtainable by the battery tester without having to remove the battery from the electronic device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The foregoing and other features and advantages of the present invention should become apparent from the following description when taken in conjunction with the accompanying drawings, in which. 
           [0008]      FIG. 1  is a rear plan view of a electric guitar body of the prior art; 
           [0009]      FIG. 2  is a schematic view of the wiring of on-board electronic tone controls of a prior art instrument, such as a guitar, and a prior art cable having an audio plug interconnecting the electric guitar to an amplifier or like apparatus; 
           [0010]      FIG. 3  is a schematic view of battery tester according to the present invention for use with on-board electronic tone controls of the instrument of  FIG. 2 ; 
           [0011]      FIG. 4  is a plan view of a first embodiment of a handheld portable battery tester according to the present invention; and 
           [0012]      FIG. 5  is a schematic view of an assembly of a guitar and a separate electronic apparatus, such as a tuner, that incorporates the battery testing circuit according to the present invention within the apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    An example of a conventional electric guitar body  10  having an access panel  12  secured to a rear of the body  10  with fasteners  14 , such as screws, is shown in  FIG. 1 . A battery compartment  12   a  is located behind the access panel  12  in close proximity to an audio jack, or receptacle,  16 . The batteries in the compartment  12   a  power the on-board electronic tone controls of the electric guitar. 
         [0014]    The wiring of typical on-board electronic tone controls  18  is shown in the upper half of  FIG. 2 . The on-board electronic tone control  18  includes a tone control circuit  20  and wiring branches  22 ,  24  and  26  electrically interconnected thereto. Battery wiring branch  22  interconnects one or more batteries  28  to a first power contact  30  of the audio jack  16 , and power wiring branch  24  interconnects the tone control circuit  20  to a second power contact  32  of the audio jack  16 . Wiring branch  26  transfers the electronic audio signals produced by the guitar to an audio contact  34  of the audio jack  16 . 
         [0015]    The lower half of  FIG. 2  illustrates an end section of a standard audio cable  36  that connects the output of the guitar to an amplifier or other apparatus (not shown). The cable  36  includes a standard audio plug  38  receivable within audio jack  16  of the guitar. The standard audio plug  38  includes an elongate, cylindrical contact  40  and an exposed audio plug tip  42 . These sections of the plugs are electrically isolated from each other, for instance, by insulator  44 . The tip  42  is connected to internal wiring (not shown) of the cable  36  that transmits the audio signal to the amplifier or like apparatus. 
         [0016]    Accordingly, when audio plug  38  is inserted into audio jack  16 , the elongate, cylindrical contact  40  electrically connects the first and second power contacts,  30  and  32 , of the audio jack  16 . This completes the power circuit and energizes the tone control circuit  20 . In addition, the audio plug tip  42  engages the audio contact  34  of the audio jack  16  thereby enabling an audio signal to be transmitted from the tone control circuit  20  to an amplifier or like apparatus connected to the opposite end of the cable  36 . 
         [0017]    The battery tester of the present invention takes advantage of the above referenced tone control circuit and wiring to enable the batteries  28  to be tested without having to remove the batteries  28  from the battery compartment  12   a  and without having to remove the access panel  12  or fasteners  14  from the guitar body  10 . The battery tester of the present invention uses the audio jack  16  to gain electrical access to the batteries  28  for purposes of determining the remaining charge level of the batteries  28 . Thus, according to the present invention, the battery tester is simply plugged into the audio jack  16  of the guitar or like instrument to obtain the desired charge level information. 
         [0018]    An example of a portable, handheld version of the battery tester  50  according to the present invention is shown in  FIG. 4 . This version of the battery tester includes a housing  52 , a display  54 , a power switch  56 , and a battery measurement plug  58  which is receivable within audio jack  16  of the guitar. 
         [0019]    The operation of the battery tester  50  is best illustrated schematically in  FIG. 3 . The upper half of  FIG. 3  shows the wiring of typical on-board electronic controls  18  discussed above, and the lower half of  FIG. 3  shows the circuitry of the battery tester  50  of the present invention. 
         [0020]    The battery measurement plug  58  can be a standard stereo plug. Accordingly, the plug  58  includes three separate contacts including a cylindrical base contact  60 , a cylindrical intermediate contact  62 , and a tip contact  64 . When plug  58  is inserted into audio jack  16 , the battery wiring branch  22  of the tone control circuit  20  is electrically connected to base contact  60  of the plug  58  and wiring  68  within the tester  50 , and the power wiring branch  32  of the tone control circuit  20  is electrically connected to intermediate contact  62  of the plug  58  and wiring  66  within the tester  50 . 
         [0021]    The tester  50  includes a high impedance input amplifier  70  that is powered by a power source  76  located in the housing  52  of the tester  50 . A high impedance input type of amplifier is required to measure battery charge level due to the effective circuit impedance  72  of the tone control circuit  20 . The high impedance input amplifier  70  is electrically connected to the wiring  66  and  68 , and this arrangement is best illustrated in  FIG. 3  and shows how the batteries  28  and the tone control circuit  20  within the guitar are electrically coupled to the high impedance input amplifier  70 . For instance, the wiring  66  interconnects the effective circuit impedance  72  and the battery  28  to a non-inverting (+) input of the amplifier  70  while wiring  68  connects to the negative side of the power source  76 . In addition, the output  78  of the high impedance input amplifier is electrically connected to the inverting (−) input of the amplifier  70  providing a voltage follower arrangement. 
         [0022]    The signal produced on the output  78  of the high impedance input amplifier  70  is proportional to battery charge level of batteries  28  and is provided to a microprocessor, A/D converter, digital display, and/or bargraph indicator circuit  74  or the like. See  FIG. 3 . According to one contemplated embodiment, the indicator circuit  74  includes a microprocessor that calculates battery charge level based on steady state level, initial peak when the tester  50  is plugged into the audio jack  16 , and/or decay of battery level signal. 
         [0023]    The display  54  of the tester  50  can be an LED or LCD and can show battery level in volts, percentage, etc. and/or can show this information in a numerical form or in the form of a bar graph. Alternatively, the tester can produce audible or other signals to indicate remaining battery charge level. Upon measurement of the battery voltage, the device can also provide an indication that the battery charge is low and should be replaced or that the battery charge is acceptable. A battery low message or alarm or a battery okay message can be displayed on the tester  50 . The tester  50  may be automatically powered when plugged into an audio jack  16  or can include a power switch  56 . Switch  56  may also be provided for selecting a mode of display of the tester  50 , such as volts, percentage, or status. 
         [0024]    As an alternative to a portable, handheld version of the battery tester of the present invention, the battery tester can also be included as part of another apparatus, such as a tuner or the like. As an example, see the assembly  80  shown in  FIG. 5 . The assembly  80  includes the guitar body  10 , a cable  82 , and electronic apparatus  84 . The guitar body  10  is identical to that discussed above with respect to  FIGS. 1 and 2 . The cable  82  includes a pair of plugs  86  that are the same as the battery measurement, or stereo, plugs  58  discussed above with respect to  FIGS. 3 and 4 . The apparatus  84  can be any guitar-related piece of electronic equipment and includes the battery testing circuitry discussed above with respect to  FIG. 3 . 
         [0025]    The apparatus  84  can include a first receptacle, or jack,  88  for receiving one of the plugs  86  of cable  82 . The opposite plug  86  of cable  82  can be plugged into the audio jack  16  of the guitar body  10 . Accordingly, for the same reasons discussed above, the battery charge level of batteries  28  of the tone control circuit  20  on-board the guitar is available for measurement by a high impedance input amplifier  90  of apparatus  84  via wiring  92  and  94  extending from the first jack  88 . See  FIG. 5 . As discussed previously, the high impedance input amplifier  90  is required to measure the battery level signal due to the effective circuit impedance  72  of the tone control circuit  20  of the guitar. The signal output by high impedance input amplifier  90  is a signal proportional to the battery charge level, and this is applied to a system microcontroller  96  having an A/D converter. As an example, the microcontroller  96  may include algorithms to calculate remaining battery charge level based on steady state charge level and initial peak and decay of battery charge level signal. 
         [0026]    After the battery charge level measurement is complete, the internal circuitry of the guitar can be powered by the actions of a switching mechanism  98 , which can be a MOSFET as illustrated, or mechanical contacts, bipolar transistor, or some other device. After the internal circuitry of the guitar is energized, the normal audio signal produced by the guitar is transmitted via tip contacts  100  of the plugs  86  of the cable  82  and by wiring  102  of apparatus  84  to the signal processor or tuner  104  of the apparatus  84 . The output of the signal processor or tuner  104  is available at output receptacle or jack  106  via use of a standard audio cable with a standard audio jack. 
         [0027]    An advantage of embodying the battery tester of the present invention as a circuit integrated into another piece of equipment, such as a tuner or effects processor, is that the microcontroller  96 , user input control keys  108 , and display  110  may all be shared as well as the housing  112  and power supply (not shown). Thus, the additional feature of battery testing can be provided at a minimum of cost. 
         [0028]    While preferred battery testers have been described in detail, various modifications, alterations, and changes may be made without departing from the spirit and scope of the present invention as defined in the appended claims.