BACKGROUND  
       [0001]     This invention relates to a hearing aid having at least one rechargeable battery, and in particular, to a recharging system that monitors the amount of charge in the battery during charging.  
         [0002]     Hearing aids having rechargeable batteries have been known in the art for a long time; e.g., see U.S. Pat. No. 3,297,933 (McCarthy). The trade-off between rechargeable batteries and non-rechargeable batteries is the inconvenience of having to replace the battery. There is also a trade-off in capacity. A non-rechargeable battery lasts much longer than a rechargeable battery having the same outside dimensions as the non-rechargeable battery. This is due to the different chemistries of the two types of batteries.  
         [0003]     The inconvenience of having to remove the battery from a hearing aid initially applied both to rechargeable batteries and non-rechargeable batteries. The sole advantage of rechargeable batteries was not having to be replaced. Then, chargers were developed that made electrical contact with the hearing aid, obviating the need to remove the rechargeable battery; e.g. see U.S. Pat. No. 3,493,695 (Stork). This simplified matters for those lacking the dexterity to remove and insert a battery. Having exposed electrical contacts is undesirable and inductive chargers solved this problem; e.g. see U.S. Pat. No. 4,379,988 (Mattatall).  
         [0004]     Inductive chargers have their own set of difficulties, including adequate coupling between the primary inductor in the charger and the secondary inductor in the hearing aid; e.g. see U.S. Pat. No. 6,658,124 (Meadows). Even with adequate coupling, rechargeable batteries are not a panacea. Most rechargeable batteries, e.g. nickel cadmium, lithium ion, and others, have “memory.” Memory in a battery relates to the amount of stored energy that it available after several discharge-charge cycles. If, for example, half the energy is used and a battery is recharged, then, eventually, only half the energy is available. Also, some rechargeable batteries do not like being overcharged, such as lithium ion batteries. These batteries overheat and rupture, sometimes violently, or catch fire. Currently, nickel-metal-hydride (NiMH) batteries are preferred for hearing aids because they have little memory and are more tolerant of overcharging.  
         [0005]     The problems of memory and overcharging are particularly acute for hearing aids because a hearing aid may partially discharge a battery during the day and then be placed on a charger overnight. If more than one hearing aid is used, the batteries may be in different states of charge but are charged simultaneously.  
         [0006]     It is known in the art that it is desirable to know the state of charge of a battery in a hearing aid; see Patent Application Publication U.S. 2003/0171787 (Money et al.). The published application refers to an “external controller” that “interrogates” a cochlear implant to determine the level of charge in a battery included in the implant.  
         [0007]     It is known in the art to use a “wireless interconnection” to program hearing aids; see U.S. Pat. No. 6,888,948 (Hagen et al.). Transferring programming data to a hearing aid is disclosed. Transferring data from a hearing aid is not disclosed in the Hagen et al. patent, nor is controlling a charging cycle by communicating with a hearing aid.  
         [0008]     In view of the foregoing, it is therefore an object of the invention to provide a rechargeable hearing aid that communicates with a charger to prevent overcharging.  
         [0009]     Another object of the invention is to provide a battery charger and hearing aid that obviate the need for careful alignment of the hearing aid in the charger for optimum inductive coupling.  
         [0010]     A further object of the invention is to provide a rechargeable hearing aid that can conduct two way communication with a charger.  
       SUMMARY OF THE INVENTION  
       [0011]     The foregoing objects are achieved by this invention in which a hearing aid having a rechargeable battery and a charger for charging the battery include means for transferring data unidirectionally or bidirectionally between the hearing aid and the charger using either a magnetic field, light, or sound. The hearing aid includes means for detecting the charge state of a battery and for sending a signal to the charger indicative of the charge state. For acoustic coupling, the charger includes a microphone and a speaker and also includes a chamber for receiving at least a portion of the hearing aid.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:  
         [0013]     The FIGURE is a partial block, partial phantom drawing illustrating a preferred embodiment of the invention. 
     
    
       [0014]     Those of skill in the art recognize that, once an analog signal is converted to digital form, all subsequent operations can take place in one or more suitably programmed microprocessors. Reference to “signal”, for example, does not necessarily mean a hardware implementation or an analog signal. Data in memory, even a single bit, can be a signal. In other words, a block diagram can be interpreted as hardware, software, e.g. a flow chart or an algorithm, or a mixture of hardware and software. Programming a microprocessor is well within the ability of those of ordinary skill in the art, either individually or in groups.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     In the FIGURE, hearing aid  10  is inserted into charger  20  for charging. Although hearing aid  10  is illustrated as the type that is inserted into the ear, the invention can be used in other types of hearing aid, such as behind-the-ear hearing aids. Hearing aid  10  includes at least one microphone, such as microphone  11 , a flex circuit or integrated circuit  12  containing a microprocessor for signal processing and other tasks, speaker  14 , and rechargeable battery  16  for power. Beneath battery  16  is inductor  17 , which is electrically coupled to circuit  12 , as are the other electrical components. Dedicated electronics can be used instead of programmable electronics but programmable electronics are preferred.  
         [0016]     The lower portion of hearing aid  10 , containing speaker  14 , fits easily within chamber  21 . The middle portion of hearing aid  10  is located in chamber  22  within inductor  23 . Inductor  17  and inductor  23  are more or less concentric but, as one of the advantages of the invention, alignment and position are not critical. The outer or upper portion of hearing aid  10  fits within conical depression  25 , which provides a self-centering action for the type of hearing aid illustrated. Conical depression  25  terminates in chamber  22 .  
         [0017]     The actual charging operation is known in the art. Energy from inductor  23  is coupled to inductor  17 , then converted to unidirectional or direct current (the current need not be steady but flows in one direction), then converted to chemical energy that is stored in the battery. Circuit  12  limits current or voltage, preferably both, to suitable values. In addition, circuit  12  monitors the condition of battery  16  to avoid overcharging. Depending upon battery type, one can monitor battery voltage or battery current during charging, interrupt charging to load the battery and monitor voltage during loading, or use other techniques, such as monitoring battery temperature, to prevent overcharging.  
         [0018]     In accordance with the invention, a signal is provided to indicate full charge, whereby charger  20  terminates the charging cycle. Such signal is a minimal communication in accordance with the invention. Preferably, signals are given indicating intermediate states of charge, whereby, for example, the rate of charging can taper off as charging nears completion. Hearing aid  10  can communicate with the charger in several media. A first medium is a magnetic field, coupling electrical signals between inductors  17  and  23 . Any frequency can be used but higher frequencies permit physically smaller inductors for a given impedance. Tens or hundreds of kilohertz are suitable. Radio frequencies can result in unlicensed emissions. Communicating by means of a magnetic field can be difficult during charging but is simpler during an interruption of the charging cycle, when the only signal on the inductors is data. A second medium is light, visible or invisible, using light emitting diode (LED) transmitters and photodiode receivers. This is not preferred because it requires additional components, requires a window in the hearing aid where space is at a premium, and consumes relatively high current for the LED transmitter in the hearing aid.  
         [0019]     The preferred medium for communication is sound, using the microphone and speaker already in the hearing aid. In accordance with a preferred embodiment of the invention, charger  20  includes speaker  31  and microphone  32  for this purpose. Given the two-way communication between the charger and the hearing aid, there is no limit on the content of the communication. For example, the charger could also serve as an interface for programming a microprocessor in the hearing aid. Using suitable tones, or sets of tones, to represent logic ones and zeros, the hearing aid can transmit a first code indicating the level of charge and a second code indicating the rate of charge. If, for example, the coupling between inductors  17  and  23  happened to be particularly good, the hearing aid could “ask” the charger to reduce the current through inductor  23  to reduce the rate of charge, thereby preventing overheating.  
         [0020]     As illustrated in the FIGURE, speaker  31  and microphone  32  are located adjacent chamber  21 . Hearing aid  10  does not form a seal with charger  20  and there is sufficient coupling between speaker  31  and microphone  11 . Speaker  31  can be located closer to microphone  11 , if desired. If one wanted the charging to be inaudible, one could position speaker  31  closer to microphone  11  and put the speaker and the hearing aid in an enclosed space.  
         [0021]     Power supply  33  provides charging power to hearing aid  10  by way of inductor  23 . A signal at a current of a few tens of milliamperes and a frequency of 200 kHz-300 kHz is effective. Power supply  33  is controlled by and communicates with microprocessor  36  by way of input-output (I/O) interface  37 . Interface  37  also drives speaker  31  and receives signals from microphone  32 . While shown as separate elements, it is known in the art that many commercially available microprocessors have analog inputs and include analog to digital (A/D) converters on the same semiconductor chip as the computer portion of the microprocessor. Thus, “microprocessor” is intended to include computing and logic capability and suitable I/O, whether on a single chip or on plural chips.  
         [0022]     As illustrated in the FIGURE, charger  20  includes receptacles for two hearing aids. Hearing aid  40  includes battery  41 , which is charged by power supply  43  under the control of microprocessor  36 . Although the operation is the same, the charging of battery  41  is completely independent of the charging of battery  16 . Hearing aid  40  does not have to be inserted into charger  20  at the same time as hearing aid  10  and need not even have the same type of battery. Communicating by way of speaker  44  and microphone  45 , the charging of battery  41  is monitored by circuit  49 . Ultimate control of the charging process is preferably in the hearing aid, which makes the system extremely flexible. Alternatively, control can be shared as desired; e.g., if memory space is limited. For example, default or starting conditions for charging can be programmed into the charger or the hearing aid can set starting conditions.  
         [0023]     The presence of a hearing aid can be detected by power supply  33  or power supply  43 , for example, by sensing a change in inductance in inductor  23  or inductor  53 . Alternatively, presence can be sensed acoustically by recognizing the sound of a hearing aid being inserted into charger  20  or by a difference in sound between microphones  32  and  45 . Other acoustic or magnetic presence detectors can be used instead. More simply, one can simply use a switch (not shown) for each receptacle to alert microprocessor  36  that a hearing aid has been inserted and to begin a charging cycle for that receptacle.  
         [0024]     The invention thus provides a rechargeable hearing aid that communicates with a charger to prevent overcharging. There is no need for careful alignment of the hearing aid in the charger for optimum inductive coupling. The communication between the hearing aid and the charger can be one-way or two-way and can include programming or other data, in addition to or instead of data for charging. Hearing aids in any state of charge can be put into the charger and be charged correctly, without any danger of overcharging or undercharging (unless removed too soon).  
         [0025]     Having thus described the invention, it will be apparent to those of skill in the art that various modifications can be made within the scope of the invention. For example, the shape of the charger and the shape of the hearing aid is not critical so long as some inductive coupling takes place for charging. As described above, the invention can be implemented in hearings aid of other forms, such as behind the ear hearing aids. Although the battery is preferably NiMH, other batteries can be used instead. For nickel cadmium batteries, a charging cycle should begin by discharging the battery to avoid memory problems. Although illustrated as below the battery, an inductor can be located in any available space within a hearing aid, including around at least a portion of the battery. An indication of partial charge can be used to terminate a charging cycle if one is unconcerned about memory problems or if the battery does not exhibit memory. Suitable indicators, such as variously colored LEDS, can be added as desired to indicate the states of operation of the charger. Even rechargeable batteries wear out. The hearing aid can be programmed to test its battery to determine whether or not the battery should be replaced; e.g. because of memory problems. This information is then sent to the charger, which can provide a suitable alarm or indication to the user. Programs can be stored temporarily or permanently in the hearing aid.
A hearing aid having a rechargeable battery and a charger for charging the battery include means for transferring data means for transferring data unidirectionally or bidirectionally between the hearing aid and the charger using either a magnetic field, light, or sound. The hearing aid includes means for detecting the charge state of a battery and for sending a signal to the charger indicative of the charge state. For acoustic coupling, the charger includes a microphone and a speaker and also includes a chamber for receiving at least a portion of the hearing aid.