Abstract:
A hearing aid includes a case and a photovoltaic cell located in the case near a translucent portion of the case. A detector circuit includes a voltage comparator for monitoring the voltage from the photocell and indicating variations in voltage. The variations are analyzed to detect data for operating the hearing aid.

Description:
This invention relates to hearing aids and, in particular, to a hearing aid in which a photovoltaic cell provides both power and communication. 
     BACKGROUND TO THE INVENTION 
     Hearing aids powered by a battery have been known for almost a century; see U.S. Pat. No 1,219,411 (Williams), for example. Modern technology has increased battery life greatly, yet it is annoying to have to replace batteries. Rechargeable batteries are a partial solution but require removal of the hearing aid and placement in a charger. Unless a user has two sets of hearing aids, the charging can be inconvenient. 
     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. 
     Using light to recharge the battery in a hearing aid is disclosed in U.S. Pat. No. 5,210,804 (Schmid) and U.S. Pat. No. 5,253,300 (Knapp). In the Schmid patent, a photovoltaic cell is behind a semi-transparent door in a hearing aid. The cell does not recharge the battery during use. At night, the door is opened and the hearing aid is placed in a stand that shines light from lamps onto the photovoltaic cell. In the Knapp patent, the photovoltaic cell is external to the hearing aid, part of a recharging case. U.S. Pat. No. 5,303,305 (Raimo et al.) discloses a hearing aid powered by a secondary battery that is recharged by a photovoltaic cell on the hearing aid. 
     It is known in the art to control or program a hearing aid using radio frequency (RF) transmissions. It is also known in the art to transmit data to a hearing aid having a diode sensitive to infrared radiation; see U.S. Pat. No. 6,229,900 (Leenen). Remote controls for hearing aids are no less likely to be misplaced or need new batteries than remote controls for any other device. It is desired to eliminate the tedium of needing a remote control. 
     GLOSSARY 
     A “primary” battery is one that is not intended for charging even though, in fact, one can safely recharge the battery one or a few times. A “secondary” battery is one that is intended for recharging a plurality of times. In general, primary batteries have a greater capacity (store more energy) than rechargeable batteries. Secondary batteries have a different internal structure from primary batteries, even when the chemistry involved is nominally the same. 
     The ordinary and accepted meaning of “translucent” is capable of transmitting light but causing sufficient diffusion to eliminate perception of distinct images. As used herein, “translucent” means capable of transmitting more than fifty percent of light incident normal to a surface. Thus, “translucent” includes media that is transparent. 
     A “speaker” generates sound from an electrical signal. In the hearing aid art, one often encounters the term “receiver” for such a device, which reads strangely to the uninitiated. “Electroacoustic transducer” is clumsy and pedantic. Thus, “speaker” is the term used for describing this invention. 
     In view of the foregoing, it is therefore an object of the invention to provide a hearing aid with a photovoltaic cell that is used for power, charging a battery, communication, and control. 
     Another object of the invention is to eliminate the need for a separate remote control. 
     SUMMARY OF THE INVENTION 
     The foregoing objects are achieved by this invention in which a hearing aid includes a case and a photovoltaic cell located in the case near a translucent portion of the case. A detector circuit includes a voltage comparator for monitoring the voltage from the photocell and indicating variations in voltage. The variations are analyzed to detect data for operating the hearing aid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates a hearing aid constructed in accordance with a preferred embodiment of the invention; 
         FIG. 2  illustrates a light gathering member adjacent a multi-junction photocell; and 
         FIG. 3  is a block diagram of a circuit for providing a plurality of functions from a photocell. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1 , hearing aid  10  includes body  11  coupled to earpiece  12  by cable  14 . Within body  11  are battery  16  and circuit board  17 . Circuit board  17  includes programmed microprocessor  18  and other circuitry for processing audio signals, charging battery  16 , and other functions. A speaker (not shown) is located in earpiece  12  and a microphone (not shown) is located in body  11 . The speaker is coupled to circuit board  17  by wires  21  in cable  14 . 
     In accordance with one aspect of the invention, hearing aid  10  includes photovoltaic cell  23  located underneath a translucent portion of case  11 . Cell  23  is electrically coupled to circuit board  17  and is both a source of power for operating the hearing aid and a source of current for recharging battery  16 . 
     Preferably, the translucent portion of case  11  is lenticular in order to increase the amount of power available from the photovoltaic cell. As illustrated in  FIG. 2 , section  31  of hearing aid  10  ( FIG. 1 ) receives translucent, lenticular member  32 . As a separate piece, it is easier to control the optical properties of member  32 . Preferably, member  32  gathers diffuse light at the wavelengths absorbed by cell  23 . 
     Member  32  is fastened to the case with a suitable adhesive. Member  32  is lenticular in the sense that light incident upon the member is redirected to a smaller angle of incidence on the underlying photovoltaic cell, as illustrated in  FIG. 4 . The light is gathered or “collimated” somewhat but not in the sense that light rays are necessarily made parallel. Member  32  preferably includes convex upper surface  34  and corrugated lower surface  35  for gathering light. To some extent, the degree of curvature of upper surface  34  depends upon the type and design of the hearing aid. 
     The lens can be cylindrical, spherical, or a compound surface. Lower surface  35  can be prismatic or Fresnel. Transparent acrylic is a preferred material for member  32 . Polycarbonate or other translucent materials can be used instead. 
     Photovolaic cell  23  is preferably what is called a multi-junction cell. For example, U.S. Pat. No. 6,252,287 (Kurtz et al.) discloses a veritable parfait of semiconductor layers in a multi-junction photovoltaic cell. Simpler designs are also usable and preferred. There are many combinations of layers possible. The band gaps of the layers are different from each other and the band gaps are arranged in descending order. Light is first incident upon the layer having the largest band gap, which absorbs at the shortest wavelength. Deeper layers absorb at progressively longer wavelengths. Output current varies with the amount of available light. 
       FIG. 3  illustrates a portion of the electronics on circuit board  17  ( FIG. 1 ). Battery  16  is charged by photovoltaic cell  23  and charger  41 . Charger  41  can operate independently of microprocessor  42  or be controlled by microprocessor  42  through bus  43 . Preferably, at a minimum, charger  41  provides data to microprocessor  42  concerning the states of battery  16  and photovoltaic cell  23 . 
     Current from cell  23  flows through series resistor  51 . A small current flows through resistor  52 , producing a voltage at junction  54  that is coupled to one input of amplifier  55 . The resistance of resistor  52  is substantially greater than, e.g. more than ten times, the resistance of resistor  51 . A second input to amplifier  55  is coupled to digital to analog converter (DAC)  53 . DAC  53  is controlled by microprocessor  42  through bus  43 . Amplifier  55  compares the voltages on the inputs and produces and output signal indicative of which input is receiving the higher voltage. This is used to monitor the current from photovoltaic cell  23 , which depends on the intensity of incident light. 
     During normal operation, the data sent to DAC  53  establishes a low threshold of incident light and the output from amplifier  55  is in a first state. When incident light falls below the threshold, the output from amplifier  55  changes to a second state. The durations of the changes in state, i.e., the periods between changes of state, are monitored by timing circuit  61 , which provides data representative of the periods to bus  43 . This data is analyzed by microprocessor  42  or by decoder  63 . Successive changes in state produce a pulse width modulated (PWM) signal from amplifier  55 . The periods of the pulses are determined by the cause of the change in light level. 
     In accordance with one aspect of the invention, a low frequency signal is interpreted as a command from the person wearing the hearing aid, who simply covers the hearing aid for a brief time to produce a pulse. This pulse can be used as a switch for functions within hearing aid  10  ( FIG. 1 ). A series of low frequency pulses can also be used to control functions of the hearing aid. Preferably, the most frequently used functions are associated with the fewest pulses. For example, switching between two levels of gain can be activated with a single pulse. Thus, if a person covers his ear for five seconds, gain is reduced by a set amount. If the person covers his ear for two or three seconds, gain is increased. The timing is made flexible by accepting wide variations in pulse width; i.e. a “window” of time is created in software in which a change of state can occur. For example, two seconds to four seconds is interpreted as a signal to increase gain, whereas a pulse must be between five seconds and seven seconds to be interpreted as a signal to decrease gain. The period analysis is done by either decode circuit  63  or microprocessor  42 . Periods that are not recognized are ignored. 
     Faster, that is higher frequency, changes in light level are interpreted by the same circuitry as command signals from a remote control. Because the photovoltaic cells are sensitive to visible light, the considerable flicker in light levels caused by fluorescent lighting, computer monitors, television sets, or other remote control units is filtered out by decode circuit  63  or microprocessor  42 . Thus, signals below approximately 5 Hz are interpreted as commands directly from a user and signals above approximately 5 Hz are interpreted as signals from a remote control. Preferably, infrared light is used for communication with a remote control but visible light can be used instead or in addition. Photovoltaic cell  23  and amplifier  55  thus provide a serial interface to a hearing aid. 
     Microprocessor  42  is programmed to execute a plurality of routines and can appear to be performing several functions simultaneously. For example, in one routine, light level is compared with a low threshold, as described above, looking for commands. If none is found, a second routine is executed in which light level is measured; e.g. by stepwise increasing the voltage from DAC  53  until amplifier  55  changes state, then reading the data that caused the transition. The search is preferably binary rather than sequential. This is known in the art as a “poor man&#39;s” analog to digital converter because other, more elegant techniques for analog to digital conversion are more complicated and more expensive. Also, it avoids adding a separate circuit for analog to digital conversion and can be faster to execute. A third routine is to monitor battery voltage through charger  41 . Circuitry (not shown) disconnects loads from battery  16  and open circuit voltage is measured and sent to microprocessor  42  over bus  43 . 
     These and other routines are not necessarily executed sequentially but can be executed in any order as determined by an executive routine or by interrupts. For example, the routine to look for commands can be executed alternately with all the other routines. 
     Returning to  FIG. 1 , hearing aid  10  includes photovoltaic cells  24  and  25 . These cells are preferably combined with photovoltaic cell  23  to increase available energy for charging or operating the hearing aid. Alternatively, photovoltaic cell  25  is used for detecting signals and cells  23  and  24  are used for power. Preferably, all cells are used for signaling but are individually monitored. Thus, for example, if cell  25  detects a very low light level of long duration and cell  23  does not, then it is likely that the user has placed a handset from a telephone against his ear. This information is used, for example, to reduce gain from microphones in the body of hearing aid  10  and turn on microphone  71  in earpiece  12 , if it were not on. 
     Case  11  and the photovoltaic cell can be combined by coating a case with a photovoltaic thin film, such as cadmium telluride (CdTe), and a protective layer over the thin film. A single film is preferred but a segmented film can be used instead depending, for example, upon the shape of the case. 
     The invention thus provides a hearing aid with a photovoltaic cell that is used for power, charging a battery, communication, and control. A separate remote control is unnecessary. 
     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, data can be sent to hearing aid  10  for setting operating parameters within the hearing aid, e.g. gain vs. frequency. The logic of the output from amplifier  55  can be inverted; i.e., the output can indicate which input is receiving the lower voltage. Any preset function can be changed by a user without the need for a remote control. For example, different patterns of correction, such as “living room,” “theater,” and “restaurant,” can be selected by covering the hearing aid for selected periods. The function of timing circuit  61  can be incorporated into microprocessor  42 . Amplifier  55  would then be coupled to an input pin of microprocessor  42 . While illustrated with separate blocks for various functions, everything but the photovoltaic cell, the charger, and the battery can be incorporated into one suitably programmed microprocessor or microcontroller. Separate blocks are illustrated for ease of understanding, not as a restriction on implementing the invention. The invention can be implemented in analog or digital, integrated or discrete form.