Abstract:
A mobile phone hand-free extension device includes a FM radio transmitter with an active frequency searching circuitry to utilize a vehicular FM radio receiver for reproducing the audio signals from the mobile phone. The active frequency searching circuitry in this invention automatically detects which frequency band the vehicular FM radio receiver is currently using and set the RF frequency of the FM transmitter to the detected frequency. The FM transmitter relays the audio signals from the mobile phone by transmitting the audio signals through radio wave to the vehicular FM radio receiver to be reproduced by the speaker of the receiver.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to a mobile phone hand-free extension device that utilizes the vehicular radio receiver to provide audio signals to the mobile phone user, and more specifically to a mobile phone hand-free extension device with a radio frequency (RF) transmitter and a frequency searching circuitry to automatically relay the audio signal received from the mobile phone to the vehicular radio receiver.  
         BACKGROUND OF THE INVENTION  
         [0002]    The technology of mobile phones has made possible mobile voice communication for millions of people. Mobile phones are carried and used daily by hundreds of millions of people and become an ordinary household items worldwide. The mobile phone user quite often makes the phone call while driving an automobile and therefore creates a potential hazardous driving condition since the driver has to hold the mobile phone and drive at the same time.  
           [0003]    A hand-free kit is an external accessory to the mobile phone and its purpose is to free the driver from distraction of holding and using the mobile phone. Several technologies have been pursued to enable the driver to use the mobile phone without holding the cellular phone.  
           [0004]    U.S. Pat. No. 6,134,456 discloses a control switch box with cables linking the mobile phones and the vehicular stereo system. However, installating such kind of accessory is quite involved and requires wiring and routing inside the automobile body.  
           [0005]    The U.S. Pat. No. 5,867,794 discloses another method that uses an FM transmitter to send the audio signal from the mobile phone to the vehicular FM radio. In the disclosure, there is no need to physically connect the mobile phone and the vehicular audio system. However, the disadvantage of this approach is that the frequency of the FM transmitter has to be set to the same channel as the FM radio receiver that the driver is currently listening to whenever he wants to use the hand-free kit. The frequency of either the FM transmitter or the FM radio receiver has to be adjusted and it causes much inconvenience in application.  
           [0006]    It will be an innovative approach to include an apparatus or a method to detect radio frequency of the FM radio receiver and to set the frequency of the FM transmitter automatically.  
         SUMMARY OF THE INVENTION  
         [0007]    This invention has been made to overcome the drawbacks of the conventional mobile phone hand-free kit. The primary object is to provide to a mobile phone hand-free extension device. The mobile phone hand-free extension device utilizes the vehicular radio receiver to provide audio signals to the mobile phone user. It includes a radio frequency (RF) transmitter and a frequency searching circuitry to automatically relay the audio signal received from the mobile phone to the vehicular radio receiver.  
           [0008]    The mobile phone hand-free extension device comprises a RF signal detector, a frequency searching circuitry and an FM transmitter. The RF signal detector detects the radio frequency communication between the mobile phone and the base station. Whenever a call activity between the mobile phone and the base station is detected by the RF signal detector, the RF signal detector activates the frequency searching circuitry to find the frequency of the FM radio receiver if the mobile phone user is listening to the FM radio. As soon as the frequency is located, the FM transmitter sends a radio wave modulated by the audio signal of the mobile phone to the FM radio receiver. On receiving the radio wave, the FM radio receiver demodulates the radio wave to retrieve the original audio signal, which is further reproduced by the speaker of the FM radio receiver. The car-driving mobile phone user therefore has no need to hold the mobile phone close to his ear since the voice and sound coming out of the mobile phone is relayed to an external speaker by this invention.  
           [0009]    Another object of the present invention is to provide a method to detect the radio frequency being tuned by a vehicular FM radio receiver and to relay the audio signal from a mobile phone to the vehicular FM radio receiver using a radio wave at the frequency detected.  
           [0010]    The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a general schematic diagram showing the audio output extension for a mobile phone hand-free operation according to the present invention.  
         [0012]    [0012]FIG. 2 shows a flow chart for automatically searching the frequency of an FM radio receiver according to the present invention.  
         [0013]    [0013]FIG. 3 shows a preferred embodiment of a mobile phone hand-free extension device using a microprocessor and a digital-to-analog converter to realize the frequency-searching unit according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    [0014]FIG. 1 is a general schematic diagram showing the audio output extension device for a mobile phone hand-free operation according to the present invention. Referring to FIG. 1, the mobile phone hand-free extension device comprises a microphone  11 , an active frequency-searching unit  12 , an FM transmitter  13 , a switch  14  and a second microphone  15 .  
         [0015]    The following describes in detail how the frequency-searching unit detects the radio frequency of the FM radio receiver and sets the frequency of the FM transmitter automatically.  
         [0016]    The active frequency-searching unit  12  controls the radio frequency of the voltage-controlled oscillator (VCO) inside the FM transmitter  13  and sends a signal with a particular pattern at the audio frequency to modulate the RF carrier of the FM transmitter. The signal sent with a particular pattern can be either a digital signal or an analog signal. The radio frequency of the FM transmitter is controlled in such a way that it starts from the lower band edge of the commercial FM band such as 88-108 MHz and increases repeatedly by a predetermined frequency step to the upper band edge. The preferred predetermined frequency step can be the allocated channel bandwidth of an FM station. At each frequency point, the FM transmitter will send out the modulated RF carrier. If the frequency of the FM transmitter matches that of the FM radio receiver  16 , the signal with a particular pattern at the audio frequency will be demodulated, retrieved and broadcasted from the speaker  17  that is connected to the FM radio receiver.  
         [0017]    The microphone  11  picks up the audio signal from the speaker and sends it to the active frequency search unit to determine if this audio signal is the same as the particular signal that the FM transmitter originally sent out.  
         [0018]    [0018]FIG. 2 shows a flow chart for automatically searching the frequency of an FM radio receiver according to the present invention. As shown in FIG. 2, the frequency stepping process, the signal emitting process, and the signal comparing process are repeated over and over again until the original signal sent out by the frequency-searching unit is received by it again. When this condition is met, the RF frequency of the FM transmitter is locked on to that of the FM radio receiver.  
         [0019]    After the RF frequency of the FM transmitter is set to that of the FM radio receiver, the switch  14  disconnects the audio signal generated by the frequency-searching unit  12  and connects the audio signal picked up by the second microphone  15  to the FM transmitter. The second microphone is placed close to the internal speaker of the mobile phone  18  to pick up the audio signal generated by the voice of the other party on the line. As a result, the audio signal is relayed to the FM radio receiver  16  and the voice is reproduced by the speaker  17 .  
         [0020]    [0020]FIG. 3 shows a preferred embodiment of a mobile phone hand-free extension device using a microprocessor and a digital-to-analog converter to realize the frequency-searching unit according to the present invention. Referring to FIG. 3, the frequency-searching unit is realized by a microprocessor-based microcontroller  21  and a digital-to-analog converter (DAC) circuitry  22 . This embodiment further includes a RF signal detector  23 .  
         [0021]    When the RF signal detector detects the signal exchange between the mobile phone  32  and the base station, it sends a signal into one of the I/O port of the microcontroller  21  to activate the frequency searching sequence.  
         [0022]    The frequency searching sequence works as follows: the microcontroller uses a plurality of I/O ports to send a parallel digital data to the DAC  22 . The number of I/O ports used corresponds to the number of bits of the digital data. The DAC converts the digital data to a corresponding analog DC voltage value. The DC voltage is used to control the oscillating frequency of the voltage-controlled oscillator inside the FM transmitter  24  and as a result the RF frequency of the FM transmitter is controlled by the microcontroller. The DAC is configured such that the minimum analog DC voltage converted from the digital data corresponds to the lower band edge of the commercial FM bands and the maximum analog DC voltage converted from the digital data corresponds to the upper band edge of the commercial FM bands. The microcontroller can increase or decrease the RF frequency of the FM transmitter by a minimum frequency step that is determined by the number of bits used for a digital data. For example, if 10 bits are used for a digital data, the step frequency will be (108-88) MHz divided by 2 10 , i.e. 19.5 KHz. The microcontroller increases the RF frequency of the FM transmitter from the lower band edge to the upper band edge or in a reverse way decreases the frequency from upper band edge to the lower band edge repeatedly by a frequency step in a programmable way to cover the whole commercial FM frequency band.  
         [0023]    At each frequency point, the microcontroller sends a beacon signal at audio frequency with a particular pattern from one of its I/O ports to the FM transmitter through the switch  25 . The pattern of the beacon signal is chosen to be different from any other possible audio signal, such as a voice signal or a noise signal from the automobile in the environment. The RF carrier modulated by the beacon signal is transmitted by the FM transmitter at the RF frequency set by the microcontroller. If the FM radio receiver  30  is working at the same RF frequency, the RF radio receiver  30  will receive and demodulate the beacon signal, which is further broadcasted by the speaker  31 .  
         [0024]    The microphone  26  picks up the beacon signal and sends it to the signal comparator  27  to determine if the received signal has the same pattern as the original beacon signal. If the signal patterns is matched, it represents a frequency locking condition, i.e. the FM transmitter and the FM radio receiver are both working at the same RF frequency channel. The switch  25  disconnects the signal path between the microcontroller and the FM transmitter, and establishes the signal path among the microphone  28 , the amplifier  29  and the FM transmitter  24 . The signal comparator  27  can be incorporated in the microcontroller  21  and implemented as a software sequence stored in the memory of the microcontroller.  
         [0025]    Therefore, the mobile phone hand-free extension device of the invention has been made to overcome the drawbacks of the conventional hand-free extension device. Its advantages include that there is no need to physically connect the mobile phone and the vehicular audio system and it can detect radio frequency of the FM radio receiver and to set the frequency of the FM transmitter automatically.  
         [0026]    Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.