Abstract:
A compressed digital music apparatus is described, which includes a cigarette-lighter power port, a headphone jack and an FM modulator/transmitter. In one mode of operation the FM modulator/transmitter modulates compressed digital music from a digital music player and then transmits the modulated music to an FM receiver. In a second mode, when a headphone is connected for personal listening the FM transmitter is disabled.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is related to concurrently filed patent applications bearing applicant docket numbers PU060058 and PU060107. 
     
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a portable audio device having a low power FM transmitter, and more particularly, to a compressed digital music transmitting device that is adaptable to disable transmission when the device is used for personal listening. 
       BACKGROUND OF THE INVENTION 
       [0003]    Due to the rapid development of the Internet and the multimedia industry and also to the insatiable human desire to be entertained, various kinds of music storage devices and broadcast systems have continued to emerge over the years. Technology has evolved from phonographic discs and phonographs, and magnetically recorded tapes and magnetic recorders in the early days, to compact discs (CDs) and digital versatile discs (DVDs), and more recently to flash memories for storing MPEG layer 3 (MP3) audio data and MP3 players. Popularity for magnetically recorded tapes has especially waned over the years because magnetic media are demagnetized easily, thereby shortening their lifetimes, and furthermore have relatively small recording capacities. 
         [0004]    MP3 audio data are compressed and stored in semiconductor memories, such as read-only memories (ROMs), erasable programmable read-only memories (EPROMs), or flash memories. Hence, an MP3 audio file usually occupies around 3 to 5 megabytes of memory, which is considerably smaller than that of a CD audio file. The music fidelity of the decoded MP3 audio data is good enough for most users. Consequently, many users convert CD audio data to MP3 audio data and store the data in computers that have MP3 players or in portable MP3 players. The MP3 players decode MP3 audio data and broadcast music. 
         [0005]    MP3 players and other digital music players possess many advantages, like being small and lightweight. Many such players have hard disk drives which allow a user&#39;s entire music collection to be stored on a pocketsized device. However, such a characteristic of portability entails that the speakers equipped with the digital music players are also small, making compressed digital music, such as MP3 music, unlikely to be broadcasted publicly. Presently, personal digital audio players are portable stand-alone units that allow a user to enjoy digital quality music with headphones or portable speakers. Many users of similar devices have a desire to listen to the digital audio player recorded music, while driving in an automobile. It can be dangerous to listen to headphones while driving and an alternative is to use a standard FM radio so that the automobile speaker system is utilized to listen to high quality digital music. Only the most expensive car radios have accessible inputs which accept the digital audio player&#39;s output. In older car radios with cassette tape players, adapters are sometimes used which fool the player into thinking a tape is in the cassette slot. In the slot is a small recoding head which makes a magnetic connection to the tape players play head. Such devices sacrifice play quality, battery life, and are problematic as most newer car radios have CD players and no tape slot. As such, there is a need for an apparatus that can receive audio signals from the digital audio player and transmit these signals through a standard FM radio. If an FM transmitter is connected to an MP3 player, for example, the player&#39;s internal battery can be drained quite quickly and require its own battery. Conventional FM transmitters in such applications may obtain operating power from a vehicle&#39;s cigarette lighter or accessory socket. 
         [0006]    It is also true that these portable devices may be used in a home environment and played through the home&#39;s FM receiver and audio system or they may be used, at another instant, as a personal player. When used as a personal player, headphones would likely be used, thus obviating the need to transmit an RF signal. It would be desirable, then, to disable the FM transmitter when headphones are connected, thus preserving battery life and avoiding a potential for FM interference. 
         [0007]    Because of the prevalence of MP3 type players that may be used either in an automobile with an FM transmitter, in a non-automobile setting using an FM transmitter or as a personal device using attached headphones or speakers, the Federal Communications Commission (FCC) of the United States has established different measurement criteria for FM transmitter radiation for use in an automobile or use outside an automobile. Radiation measurements are specified to be made of the field strength at a distance of three meters from a radiating device. Since the FCC bases the measurement criteria on the realistic use of a device, the measurement criteria for a device only to be used in an automobile may be three meters from the automobile while the measurement criteria for a device to be used outside an automobile must be three meters from the device. This difference in measurement method allows the power radiated from the transmitter to be increased by approximately 6 dB when it can be shown that the device is to be operated only in an automobile. It is clear, then, that an opportunity exists to more finely optimize operation of portable MP3-like devices. 
         [0008]    The MP3 music and MP3 players mentioned are only examples to illustrate the embodiments conveniently and are not proposed to limit the present invention. The apparatus according to the invention can adapt to or integrate with other types of digital music players as well as modulate other formats of compressed digital music, such as that of code excited linear prediction (CELP), window media audio (WMA), and advanced audio coding (AAC), without departing from the scope and the spirit of the invention. Although we generally refer to auto or automobile, it should be understood that these terms are intended to encompass a broad range of vehicular conveyance. 
       SUMMARY OF THE INVENTION 
       [0009]    In accordance with one aspect of the present invention, there is provided an apparatus comprising an interface configured to receive an audio signal, a transmitter configured to receive the audio signal from the interface and transmit a radio frequency signal containing the audio signal to a first device, a connector for providing the audio signal to a second device and a detector configured to disable the transmitter when the second device is connected to the connector. In another embodiment of the invention the first device may be a radio frequency receiver or possibly an FM radio frequency receiver and the transmitter may comprise a frequency modulator. In a further refinement of the invention the second device may be a headphone or a loudspeaker. In another embodiment the detector comprises a switch, possibly integral to the connector. The detector may also be an electronic device for detecting the impedance associated with the second device. The audio signal in these embodiments may be an MP3 encoded signal. 
         [0010]    In accordance with another aspect of the invention, there is described a method comprising the steps of detecting the presence of an external device when the external device is connected to an audio player, disabling transmission of a carrier frequency modulated with audio signals from the audio player when the external device is connected to the audio player and enabling transmission of the carrier frequency when the external device is not connected to the audio player. One embodiment of the invention comprises the step of frequency modulating the carrier frequency. A further aspect of the invention comprises sensing the presence of the external device by detecting the mechanical connection of the external device or alternatively by detecting the presence of the external device by detecting the electrical impedance of the external device. 
         [0011]    A further embodiment comprises means for transmitting a modulated signal from an apparatus to a first device, means for determining if a second device is connected to the apparatus and means for enabling the means for transmitting when the second device is not connected to the apparatus. A further aspect of the invention further comprises means for obtaining operating power from an external source, perhaps by means of a cigarette lighter plug. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    For a better understanding of the present invention, reference is made to the accompanying drawings. Reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawings. 
           [0013]      FIGS. 1 and 2  describe two different views of an embodiment of an audio player having integral transmitter and cigarette lighter plug. 
           [0014]      FIG. 3  describes in block diagram and schematic form, a system for disabling a transmitter when headphones are connected, for increasing the radiated RF signal from an included FM transmitter when the portable device is used in an automobile environment and for selecting various radiating elements. 
           [0015]      FIGS. 4 and 5  show details of a headphone jack with an integral switch for detecting a plug not inserted ( FIG. 4 ) or a plug inserted ( FIG. 5 ) into an audio output jack. 
           [0016]      FIG. 6  details, in block diagram form, an alternative circuit for detection of connection of headphones. 
           [0017]      FIGS. 7 and 8  demonstrate examples of an embodiment of a cigarette lighter plug for detecting if the plug is not inserted in a receptacle ( FIG. 7 ) or is inserted in a receptacle ( FIG. 8 ). 
           [0018]      FIGS. 9 and 10  are block diagrams helping to explain the radiation mechanisms of some embodiments of the invention. 
           [0019]      FIG. 11  shows a flow chart of a method of disabling a transmitter associated with a portable audio device when headphones are connected to the device. 
           [0020]      FIG. 12  shows a flow chart of a method of adjusting the power of a transmitter depending on the environment of operation of an audio player and transmitter. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    For broadcasting MP3 audio in an automobile or other environments by means of a transmitter to automobile or more stationary receiving equipment, the apparatus and methods for vehicles in accordance with the preferred embodiments of the present invention are disclosed in detail as follows, taken in conjunction with the accompanying drawings. 
         [0022]      FIG. 1  shows an end view of audio player  100  which is housed in a case  102  which has an integral cylindrical cigarette lighter type plug  104 . Contained within plug  104  are retaining ears  106  for holding plug  104  in place when inserted into a mating socket. Also co-axial to plug  104  is a spring-loaded positive power connector  108  and negative supply terminals  110 .  FIG. 2  is a front view of audio device  100  and shows, in addition to features  102 - 110 , a transmitter frequency selector  112 , operational controls  114 - 120 , a headphone output connector  122 , a memory card  124  containing audio source material and a Universal Serial Bus connector  126  for alternative audio source data. 
         [0023]    Looking now to  FIG. 3 , cigarette lighter plug  104  is shown to contain +12 V. plunger  108 , a detector  302  and a fuse  304 . When plug  104  is inserted into a mating socket, in one embodiment plunger  108  makes contact with the 12 volt power system of the vehicle. When plug  104  is inserted into a mating socket, +12 volts from the vehicle power system powers voltage regulator  348  which provides, usually, about +5 volts to power included circuits. The voltage output from regulator  348  forward biases diode  334  and provides operating voltage to the audio and transmitter circuits. If the portable device is operated from an internal 3 volt battery, or equivalent,  338 , and +12 volts is not applied to plunger  108 , diode  336  is forward biased, supplying operating voltage. In this way, battery  338  is used only when plunger  108  is not providing input power. As plunger  108  is compressed against an internal spring, detector  302  senses insertion of the plug  104  into the socket. A signal, P DETECT, is output from detector  302  and signals power switch  328  to increase the RF power delivered to antenna switch  340  when plug  104  is inserted in its mating socket. Power switch  328  may operate in any of a number of ways known to those skilled in the art; such as a gain controlled amplifier, a switched attenuator or a switched capacitor interposed between the transmitter  326  and antenna switch  340 . Plug  104  also contains vehicle ground connection  110  to connect the portable device to the vehicle ground  306 . Detector  302  could also operate by detecting compression of ground contacts  110  or by electrically detecting the presence of the 12 volt supplied from plunger  108 . Audio source device  320 , for example an MP3 player, contains audio source and processing circuitry  322  and amplifier  324 . Audio source and processing device  322  may use SD, MMC or USB source data from a memory  350  or from an Aux audio input  352 . Audio source device  320  outputs a line level output, LINE OUT, as an input to FM transmitter  326  and a volume controlled output, CONTROLLED OUT, to amplifier  324 . Amplifier  324  is a headphone driver amplifier, its output signals RIGHT OUT and LEFT OUT being connected to headphone jack  312 . Headphone jack  312  in one embodiment is of a type having a switch  314  to mechanically sense if a headphone plug is inserted. If headphones  318  are inserted, this condition is signaled to switch  310  by the signal HP DETECT. Switch  310  operates to apply operating voltage to FM transmitter  326  when no headphones are connected to headphone jack  312  and to remove operating voltage from transmitter  326  when headphones are connected. Audio source device  320  and FM transmitter  326  are powered from operating voltage supply  308  and circuit ground  332 . Capacitor  346  is a power supply bypass capacitor for the audio source device  320 , FM transmitter and other related processing circuits. Low-pass filters (LPF)  342  and  344  may be used to isolate the automobile DC power source, as input by plug  104 , at RF frequencies to facilitate use of the automobile +12 volt wiring or the automobile&#39;s chassis, which is connected to the negative terminal of the automobile DC power source, as RF radiating elements in some embodiments. Antenna switch  340  is used in some embodiments to select among the automobile&#39;s +12 volt wiring, the automobile&#39;s chassis or a separate antenna  330  as the RF radiating element for the FM transmitter. Antenna switch  340  may route signals RF OUT  1 , RF OUT  2  or RF OUT  3  to selected radiators. 
         [0024]      FIGS. 4 and 5  detail the construction of headphone jack  314 . In  FIG. 4  headphone plug  418  is not inserted into jack  314  and in  FIG. 5 , jack  314  and plug  418  are mated. In  FIG. 4 , when plug  418  is removed from headphone jack  312 , switch  314  is closed and in  FIG. 5 , when plug  418  is inserted into jack  312 , switch  314  is open. Switch  314 , comprising contacts  412  and  414 , is held closed when plug  418  is removed. Contacts  412  and  414  are held closed by the action of leaf spring  410  acting against rigid leaf  408 . When plug  418  is inserted into jack  312 , leaf spring  410  is deflected by insulator  416  which rigidly connects leaf spring  410  and spring contact  406 . As switch contacts  412  and  414  are affixed to spring contact  406  and leaf spring  410  respectively, they open or close switch  314  as plug  418  is inserted or removed. Headphone jack  312  also comprises spring contact  406  for contacting tip  420  of phone plug  418 , spring contact  402  for contacting ring  422  of plug  418  and spring contact  404  for contacting shank  424  of plug  418 . Tip  420 , ring  422  and shank  424  are connected to the left earpiece, right earpiece and ground, respectively, of headphones  318 . In a monaural system, tip  420  would contact both earpieces and ring  422  would not be used. In a manner as previously described, switch  314  is opened when the plug from an external headphone  318  or speaker is inserted into the receptacle  312 , and is closed when no such plug is inserted. In this manner, operating power can be removed from the FM transmitter circuit  326  if the plug of an external earphone  318  or speaker is inserted into the receptacle  312 . 
         [0025]      FIG. 6  illustrates an alternative embodiment for removing power from FM transmitter  326  when headset  318  is connected to output jack  606 . Since jack  606  does not include a mechanical switch, in the embodiment of  FIG. 6 , the DC impedance of headphone  318  is measured to sense the connection. The typical DC impedance of a headphone earpiece is 32 Ohms, so by placing resistor  604  between the voltage supply  338  and the left earpiece connection  608 , a detector  602  will see 12 volts at its input if no earphone is connected to jack  606  and will see a lower voltage, the divider ratio of 32 ohms to the value of resistor  604 , at its input when a headphone is connected. Detector  602  output can then operate switch  310  to either apply or remove the supply voltage to FM transmitter  326 . In this embodiment, connection of resistor  604  and detector  602  to the left audio output is desirable to accommodate both stereo and mono systems. 
         [0026]      FIGS. 7 and 8  describe the details of the mechanical construction of an embodiment of detector  302  in a cigarette lighter type plug  104 . Plunger  108  is shown in  FIG. 7  in its neutral state wherein spring  706  has extended plunger  108  outward, as when plug  104  is not inserted into a mating socket. In the condition of  FIG. 7  a switch formed by-spring contacts  702  and  704  is open and no voltage is applied to either switch contacts  702  or  704 . When plug  104  is inserted into a mating socket, +12 volts is applied to plunger  108  from the vehicle&#39;s battery and plunger  108  is moved into the body of plug  104 , operating against spring  706 . +12 volts is applied to spring contact  702  to supply operating voltage to the portable device. +12 volts is also applied to spring contact  704 , which in this embodiment provides detector output P DETECT. One could develop signal P DETECT directly by detecting +12 volts supplied to the audio circuits, but by incorporating switch contact  704  to sense the compression of plunger  108 , it becomes more difficult for a user to subvert the rules of allowable power by applying +12 volts to plunger  108  without inserting plug  104  into a mating socket. 
         [0027]    With the aid of  FIGS. 9 and 10 , we will describe mechanisms by which the FM transmitter  326  may radiate the RF out signal in several embodiments. In one embodiment shown in  FIG. 9 , low-pass filter  342  is interposed between operating supply voltage terminal  912  and the positive terminal  910  of the automobile DC power source represented as  906 . The signal RF OUT  920  from FM transmitter  326  is then connected by connection  918  to automobile power source positive terminal  910 . Element Z+, item  902 , represents the radiation impedance between the automobile&#39;s +12 volt wiring and earth ground  916 . If the impedance of LPF  342  at the frequency of signal RF OUT is significantly higher than radiation impedance  902 , the auto&#39;s +12 volt wiring will be a very effective electrostatic radiating antenna. In a different embodiment, shown by dashed line  918 ′ connecting RF OUT from FM transmitter  326  to negative terminal  908  of DC power source  906 , RF signals are coupled to negative terminal  908  of DC power source  906 , isolated from operating supply voltage negative terminal  914  by LPF  344 . In a manner similar to that previously presented, if the impedance of LPF  344  is large compared to the radiation impedance  904  from the automobile chassis to earth ground, then the entire car can become the radiating antenna. 
         [0028]    In  FIG. 10  the signal RF OUT is connected directly to supply voltage negative terminal  914  without the isolation of LPF  344 . In this embodiment signal RF OUT produces a loop current i RF  flowing from FM transmitter output terminal  920  through the low impedance formed by the FM transmitter negative return connection  914  and bypass capacitor  346 . This current flowing in such a low impedance loop favors generation of a magnetic field radiation antenna where the radiation from the +12 volt or chassis ground embodiments shown in  FIG. 9  favors generation of an electric field. A significance of the difference in type of field favored by embodiments of  FIG. 9  compared to embodiments of  FIG. 10  is the rate at which field strength attenuates as a function of distance from the radiator. A magnetic field attenuates proportionally to the inverse of the cube of distance from the radiator whereas an electric field attenuates proportionally to the inverse of the square of the distance. Use of a structure that optimizes radiation of a magnetic field can allow use of a higher field strength in the immediate vicinity of the FM receiver&#39;s antenna while maintaining a prescribed level 3 meters from the automobile. Comparing equal field strength at 3 meters from the automobile from an electric field generator and from a magnetic field generator, the field strength at 1 meter from the portable device will be greater for the magnetic field generator. This is a decided benefit for the magnetic field generator since the field strength at the FM receiver&#39;s antenna is maximized while still complying with the FCC regulations. An alternative embodiment is also shown in  FIG. 10  wherein the signal RF OUT is connected to the positive supply  912  of FM Transmitter  326 , generating loop current i RF ′. 
         [0029]      FIG. 11  describes a method of disabling a transmitter of a portable device if a headphone or speaker is connected to an output jack. The method comprises starting at step  1102 , connecting audio from an audio source device to an FM transmitter at step  1104 , connecting audio from an audio source device to an external headphone/speaker jack at step  1106 , determining if a headphone or speaker is connected to the jack at step  1108  and enabling transmission from the transmitter if a headphone or speaker is not connected to the output jack at step  1110  or disabling transmission from the transmitter if a headphone or speaker is connected to the output jack at step  1112 . 
         [0030]      FIG. 12  describes a method of controlling the power level from a transmitter comprising starting at step  1202 , connecting audio from an audio source device to an FM transmitter at step  1204 , connecting audio from an audio source device to an external headphone/speaker jack at step  1206 , determining if the transmitter is powered from an automobile cigarette lighter type socket at step  1208  and enabling transmission from the transmitter at a higher level if the transmitter is powered from an automobile cigarette lighter type socket at step  1210  or enabling transmission from the transmitter at a lower power level if the transmitter is not powered from an automobile cigarette lighter type socket at step  1212 . 
         [0031]    Free field radiation measurements indicate that by measuring the transmitter field strength at 3 meters from an automobile, the radiated power from the transmitter can be increased by 6 to 7 dB vertically and about 20 dB over the condition of free field radiation at 3 meters from the portable device. This provides a significant improvement in performance for operation in a vehicular environment. 
         [0032]    While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed, rather the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.