Patent Publication Number: US-2009239465-A1

Title: Doorphone system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a doorphone system. 
     2. Description of Related Art 
     Conventionally, there is known a doorphone system capable of responding to a visitor by bidirectionally transmitting and receiving a sound (voice) between a doorphone entrance station arranged at an entrance and a doorphone master station arranged in a house. In Patent Reference-1, there is disclosed a technique for executing mutual talk between a wire interphone system and a wireless interphone system by mounting a relay adapter for cordless interphone on a main phone in a wire interphone system, for example. In Patent Reference-2, there is disclosed a wireless interphone system which is formed by combining a wireless relay station to which the doorphone entrance station is connected with using a signal line, a wireless interphone and a wireless call device. 
     In addition, there is known a doorphone system which is connected to a cordless phone. In Patent Reference-3, there is disclosed a doorphone system which is formed by combining a cordless phone including a wireless transmitting/receiving unit capable of receiving a call signal from the doorphone to realize the talk with the doorphone, for example. In Patent Reference-4, there is disclosed a technique related to the present invention, too. 
     However, in the techniques according to Patent References-1 and 2, basically, the doorphone master station and the cordless phone extension master station (cordless/wireless interphone) form a master-sub relationship and directly execute wireless communication. Therefore, a communicatable range tends to be limited within an electric wave arrival range between the doorphone master station and the cordless phone extension master station. Meanwhile, in the techniques according to Patent References-3 and 4, it is difficult to easily form a new communication system by adding the cordless phone to the doorphone system. 
     Patent Reference-1: Japanese Utility Model Laid-open under No. H05-33094 
     Patent Reference-2: Japanese Patent Application Laid-open under No. 2002-252711 
     Patent Reference-3: Japanese Patent Application Laid-open under No. H11-136373 
     Patent Reference-4: Japanese Patent No. 2855922 
     SUMMARY OF THE INVENTION 
     The present invention has been achieved in order to solve the above problem. It is an object of the present invention to provide a doorphone system which can enlarge a communicatable range by making a relay station as a master station and establishing a wireless communication link, and which can conveniently form a system formed by combining a cordless phone. 
     According to one aspect of the present invention, there is provided a doorphone system including: a doorphone entrance station; a doorphone master station which is connected to the doorphone entrance station via a wire; a relay station which is wirelessly connected to the doorphone master station; a cordless extension master station which is wirelessly connected to the relay station, wherein a wireless communication link is established between the doorphone master station and the cordless extension master station via the relay station. 
     The above doorphone system is preferably used in order to respond to a visitor by bidirectionally transmitting and receiving a sound between the doorphone entrance station and the doorphone master station. Concretely, the doorphone system includes the relay station, and the doorphone master station and the relay station are wirelessly connected. The relay station and the cordless extension master station are wirelessly connected. Then, via the relay station, the wireless communication link between the doorphone master station and the cordless extension master station is established. Namely, all the wireless communication between the doorphone master station and the cordless extension master station is executed via the relay station. According to the above doorphone system, since the wireless communication link is established with using the relay station, the communicatable range between the doorphone master station and the cordless extension master station can be effectively enlarged, compared with such a system that the doorphone master station and the cordless extension master station form an extension relation and the wireless communication is directly executed. 
     In a preferred manner of the above doorphone system, the doorphone master station may include a first wireless unit which wirelessly communicates with the relay station; the cordless extension master station may include a third wireless unit which wirelessly communicates with the relay station; and the relay station may include a circuit control unit which functions as a master station against each of the first wireless unit and the third wireless unit, and may include a second wireless unit which wirelessly communicates with each of the first wireless unit and the third wireless unit. In this case, in the doorphone system, the relay station functions as a wireless master station, and the doorphone master station and the cordless extension master station function as wireless extension master stations. Thereby, the wireless communication link is formed. 
     In a manner of the above doorphone system, the relay station may include a charging unit which charges the cordless extension master station. In this manner, the relay station can function as the wireless master station in the wireless communication link, and can function as the charging device of the cordless extension master station. Further, the relay station can be easily carried, and a mounting position thereof can be easily moved in correspondence with a wave situation. 
     In another manner of the above doorphone system, the relay station may include a telephone line interface circuit which operates as a cordless phone. 
     In this manner, the cordless phone functions as the wireless master station, and the doorphone master station and the cordless extension master station function as wireless extension master stations. Thereby, the wireless communication link is formed. Namely, via the cordless phone, the wireless communication link between the doorphone master station and the cordless extension master station is established. In the above doorphone system, the wireless master station is regarded as a single device in the wireless communication system. For example, compared with a system including two wireless master stations such as the doorphone master station and the cordless phone master station, the above doorphone system does not have to implement a special protocol. Therefore, the system formed by combining the doorphone system and the cordless phone can be easily formed. In addition, the system including the cordless phone extension master station can make the cordless phone extension master station as the cordless extension master station. 
     In still another manner of the above doorphone system, the relay station may be formed so that an ON/OFF state of a wireless communication function is switchable. 
     In accordance with this embodiment, when a new doorphone system is formed by adding the cordless phone to the doorphone system including the relay station, the wireless communication function in the relay station is made in the OFF state, and the master-sub relationship among the doorphone master station, the cordless extension master station and the cordless phone is registered again. Thereby, the new system can be conveniently formed. 
     The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiment of the invention when read in conjunction with the accompanying drawings briefly described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing a system configuration of a doorphone system according to a first embodiment; 
         FIG. 2  is a block diagram showing the entire configuration of the doorphone system according to the first embodiment; 
         FIG. 3  is a flow chart showing a process executed by a doorphone entrance station and a doorphone master station in the first embodiment; 
         FIG. 4  is a flow chart showing a process executed by a relay station in the first embodiment; 
         FIG. 5  is a flow chart showing a process executed by a cordless extension master station in the first embodiment; 
         FIG. 6  is a schematic diagram showing a system configuration of the doorphone system according to a modification of the first embodiment; 
         FIG. 7  is a schematic diagram showing a system configuration of a doorphone system according to a second embodiment; 
         FIG. 8  is a block diagram showing the entire configuration of the doorphone system according to the second embodiment; 
         FIG. 9  is a flow chart showing a process executed by the doorphone entrance station and the doorphone master station in the second embodiment; 
         FIG. 10  is a flow chart showing a process executed by a cordless phone master station in the second embodiment; and 
         FIG. 11  is a flow chart showing a process executed by a cordless phone extension master station in the second embodiment. 
     
    
    
     BRIEF DESCRIPTION OF THE REFERENCE NUMBER 
     
         
         
           
               1  Doorphone entrance station 
               2  Doorphone master station 
               3 ,  3   a  Relay stations 
               4 ,  4   a ,  4   b ,  4   c  Cordless extension master stations 
               6  Cordless phone master station 
               7  Cordless phone extension master station 
               27 ,  31 ,  41 ,  61 ,  71  Wireless units 
               101 ,  101   a ,  102  Doorphone systems 
           
         
       
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will now be described below with reference to the attached drawings. 
     First Embodiment 
     First, a description will be given of a doorphone system according to a first embodiment of the present invention.  FIG. 1  is a schematic diagram showing a system configuration of a doorphone system  101  according to the first embodiment. 
     The doorphone system  101  mainly includes a doorphone entrance station  1 , a doorphone master station  2 , a relay station  3  and a cordless extension master station  4 . Basically, the doorphone system  101  is a system which bidirectionally transmits and receives the sound between the doorphone entrance station  1  and the doorphone master station  2  or the cordless extension master station  4  to be able to respond to a visitor. 
     The doorphone entrance station  1  is provided out of a house (e.g., at an entrance), and the doorphone master station  2  is provided in the house (e.g., in a living room). The doorphone entrance station  1  and the doorphone master station  2  are connected via a signal line L In a two-wire system, and the communication is executed by the signal line L. The doorphone master station  2  and the relay station  3  are wirelessly connected, and the relay station  3  and the cordless extension master station  4  are wirelessly connected. Concretely, in the doorphone system  101 , the relay station  3  functions as the wireless master station phone, and the doorphone master station  2  and the cordless extension master station  4  function as the wireless extension master station. Thereby, the wireless communication link is formed. Namely, via the relay station  3 , the wireless communication link between the doorphone master station  2  and the cordless extension master station  4  is established. Thereby, all of the wireless communication between the doorphone master station  2  and the cordless extension master station  4  is executed via the relay station  3 . 
     The relay station  3  is formed to charge the cordless extension master station  4 . Namely, the relay station  3  includes a charging unit (not shown) having a function to charge the cordless extension master station  4 . For example, the relay station  3  is formed as a charge mount capable of retaining the cordless extension master station  4  on its upper portion. In addition, the relay station  3  is formed so that an ON/OFF state of the wireless communication function is switchable by a switch. 
       FIG. 2  is a block diagram showing the entire configuration of the doorphone system  101  according to the first embodiment. As described above, the doorphone system  101  includes the doorphone entrance station  1 , the doorphone master station  2 , the relay station  3  and the cordless extension master station  4 . 
     The doorphone entrance station  1  includes a microphone  11 , a speaker  12 , a call button  13  and a multiplexing circuit  14 . The microphone  11  collects the sound (voice) of the visitor, and the speaker  12  outputs the sound of the user (the person in the house). The call button  13  is pushed when the visitor makes a call. The multiplexing circuit  14  processes the sound signal and the signal corresponding to the operation of the call button  13 , and inputs and outputs the signal to and from the doorphone master station  2  via the signal line L. Concretely, the multiplexing circuit  14  transmits, to the doorphone master station  2 , a signal (hereinafter referred to as “call signal”) corresponding to the push of the call button  13  when the visitor pushes the call button  13 . In addition, the signal corresponding to the sound of the visitor, collected by the microphone  11 , is inputted to the multiplexing circuit  14 , and the multiplexing circuit  14  transmits the signal to the doorphone master station  2 . Further, the multiplexing circuit  14  receives the signal corresponding to the sound of the user from the doorphone master station  2  to output the signal to the speaker  12 . 
     The doorphone master station  2  includes a multiplexing circuit  21 , a sound signal processing unit  22 , a microphone  23 , a speaker  24 , an operation unit  25 , a control unit  26 , a wireless unit  27  and an antenna  28 . The multiplexing circuit  21  is controlled by the control unit  26 , and inputs and outputs the sound signal to and from the sound signal processing unit  22 . The sound signal processing unit  22  modulates and demodulates the sound signal. The microphone  23  collects the sound of the user. The speaker  24  outputs the sound of the visitor, and generates a call sound when the call signal is received from the door phone entrance station  1 . The operation unit  25  includes various kinds of buttons (not shown), and it is operated when the user performs the talk via the doorphone master station  2  and when the user finishes the talk via the doorphone master station  2 . The signal from the operation unit  25  is inputted to the control unit  26 , and the control unit  26  controls the multiplexing circuit  21 , the sound signal processing unit  22  and the wireless unit  27 . 
     The wireless unit  27  is formed to be wirelessly communicatable with the relay station  3  via the antenna  28 . Concretely, the wireless unit  27  functions as an extension master station against the wireless unit  31  in the relay station  3  (i.e., the wireless unit  31  functions as a master station), and executes the wireless communication. In details, at the time of receiving the call signal from the doorphone entrance station  1 , by transmitting the call signal to the relay station  3  via the antenna  28 , the wireless unit  27  establishes the wireless communication link with the relay station  3 . In this manner, the wireless unit  27  corresponds to a first wireless unit. 
     The relay station  3  includes the wireless unit  31 , an antenna  32  and a circuit control unit  33 . The wireless unit  31  can wirelessly communicate with the wireless unit  27  in the doorphone master station  2  and the wireless unit  41  in the cordless extension master station  4  by its circuit control via the antenna  32 . Concretely, the circuit control unit  33  is integrated with the wireless unit  31 , and the wireless unit  31  functions as a master station against the wireless units  27  and  41  (namely, the wireless units  27  and  41  function as extension master stations). Thus, the wireless communication is executed. Thereby, the wireless communication becomes possible between the doorphone master station  2  and the cordless extension master station  4  via the relay station  3 . Specifically, at the time of receiving the call signal from the doorphone master station  2 , by transmitting the call signal to the cordless extension master station  4  via the antenna  32 , the wireless unit  31  establishes the wireless communication link with the cordless extension master station  4 . In this manner, the wireless unit  31  corresponds to a second wireless unit. 
     The cordless extension master station  4  includes the wireless unit  41 , a sound signal processing unit  42 , a microphone  43 , a speaker  44 , a control unit  45 , a talk button  46 , an end button  47  and an antenna  48 . The microphone  43  collects the sound of the user. The speaker  44  outputs the sound of the visitor, and generates the call sound at the time of receiving the call signal from the relay station  3 . The talk button  46  is pushed when the user performs the talk by the cordless extension master station  4 . The end button  47  is pushed when the user finishes the talk by the cordless extension master station  4 . The sound signal processing unit  42  executes modulation/demodulation of the sound signal. The signal is inputted to the control unit  45  from the talk button  46  and the end button  47 , and the control unit  45  controls the sound signal processing unit  42  and the wireless unit  41 . 
     The wireless unit  41  can wirelessly communicate with the relay station  3  via the antenna  48 . Concretely, the wireless unit  41  functions as an extension master station against the wireless unit  31  in the relay station  3  (i.e., the wireless unit  31  functions as a master station), and the wireless communication is executed. In details, when the wireless unit  41  receives the call signal from the relay station  3  and the talk button  46  is pushed, the wireless unit  41  establishes the wireless communication link with the relay station  3 . Thereby, the wireless communication link is established among the doorphone master station  2 , the relay station  3  and the cordless extension master station  4 . Namely, the sound link is formed among the doorphone entrance station  1 , the doorphone master station  2 , the relay station  3  and the cordless extension master station  4 . Thereby, it becomes possible that the visitor and the user have a conversation between the doorphone entrance station  1  and the cordless extension master station  4 . As described above, the wireless unit  41  corresponds to a third wireless unit. 
     Now, the doorphone system  101  according to the first embodiment will be compared with a system (hereinafter referred to as “doorphone system according to a first comparative example”) having a master-sub relationship between the doorphone master station and the cordless extension master station, which directly executes the wireless communication. In the doorphone system according to the first comparative example, the communicatable range is limited within the range of electric wave arrival between the doorphone master station and the cordless extension master station. Meanwhile, in the doorphone system  101  according to the first embodiment, the wireless communication link is established by making the relay station  3  function as a wireless master station. Thus, by providing the relay station  3  at an appropriate position between the doorphone master station  2  and the cordless extension master station  4 , it becomes possible that the communicatable range according to the first embodiment is enlarged more than that of the first comparative example. It becomes possible that a new system is formed by adding the device such as the relay station  3  to the doorphone system according to the first comparative example. However, in that case, it is necessary that both of the doorphone master station and the cordless extension master station implement a special communication protocol corresponding to a device for relaying communication, and it is also necessary to switch whether the doorphone master station functions as a wireless master station having a circuit exchanging function or as a wireless extension master station having no circuit exchanging function, dependently on existence or no-existence of the relay station. Therefore, the new system is less convenient than the doorphone system  101  including the system originally having the relay station  3 , and the new system becomes complicated, which increases the cost. 
     Next, a description will be given of a process executed in the doorphone system  101 , with reference to  FIG. 3  to  FIG. 5 . 
       FIG. 3  is a flow chart showing a process executed by the doorphone entrance station  1  and the doorphone master station  2 . In  FIG. 3 , the main body (the doorphone entrance station  1  or the doorphone master station  2 ) which executes the process in each step is shown in each parenthesis. Additionally, the process is repeatedly executed. 
     First, in step S 101 , the doorphone entrance station  1  determines whether or not the visitor pushes the call button  13 . When the call button  13  is pushed (step S 101 ; Yes), the process goes to step S 102 . Meanwhile, when the call button  13  is not pushed (step S 101 ; No), the process returns to step S 101 . 
     In step S 102 , the doorphone master station  2  executes the process for calling the relay station  3 . Concretely, since the call button  13  is pushed (step S 101 ; Yes), the doorphone master station  2  receives the call signal from the doorphone entrance station  1  to transmit the call signal to the relay station  3 . Then, the process goes to step S 103 . In step S 103 , the doorphone master station  2  establishes the wireless communication link with the relay station  3 . Concretely, by the control of the circuit control unit  33  in the relay station  3 , the doorphone master station  2  and the relay station  3  communicate with each other. Thereby, the wireless communication link is established. Then, the process goes to step S 104 . 
     In step S 104 , the doorphone master station  2  cuts the wireless communication link with the relay station  3 . Concretely, when the user pushes the end button  47  (for terminating communication) of the cordless extension master station  4  and the wireless communication link between the relay station  3  and the cordless extension master station  4  is cut, the doorphone master station  2  cuts the wireless communication link with the relay station  3 . In this case, by the control of the circuit control unit  33  in the relay station  3 , the doorphone master station  2  and the relay station  3  communicate with each other. Thereby, the wireless communication link is cut. Afterward, the doorphone master station  2  moves to a waiting state. When the above process ends, the process goes out of the flow. 
       FIG. 4  is a flow chart showing a process executed by the relay station  3 . The process is repeatedly executed. 
     First, in step S 201 , the relay station  3  determines whether or not it receives the call from the doorphone master station  2 . Namely, the relay station  3  determines whether or not it receives the call signal from the doorphone master station  2 . In the above process in step S 102  (see  FIG. 3 ), the doorphone master station  2  transmits the call signal to the relay station  3 . When the relay station  3  receives the call from the doorphone master station  2  (step S 201 ; Yes), the process goes to step S 202 . Meanwhile, when the relay station  3  does not receive the call (step S 201 ; No), the process returns to step S 201 . 
     In step S 202 , since the relay station  3  receives the call from the doorphone master station  2 , the relay station  3  establishes the wireless communication link with the doorphone master station  2 . Concretely, by the control of the circuit control unit  33  in the relay station  3 , the doorphone master station  2  and the relay station  3  communicate with each other. Thereby, the wireless communication link is established. Then, the process goes to step S 203 . In step S 203 , the relay station  3  executes the process for calling the cordless extension master station  4 . Concretely, the relay station  3  transmits the call signal to the cordless extension master station  4 . Then, the process goes to step S 204 . 
     In step S 204 , the relay station  3  establishes the wireless communication link with the cordless extension master station  4 . Concretely, by the control of the circuit control unit  33  in the relay station  3 , the relay station  3  and the cordless extension master station  4  communicate with each other. Thereby, the wireless communication link is established. Then, the process goes to step S 205 . 
     In step S 205 , the relay station  3  cuts the wireless communication link with the cordless extension master station  4 . Concretely, when the user pushes the end button  47  of the cordless extension master station  4 , the relay station  3  releases the wireless communication link with the cordless extension master station  4 . In this case, by the control of the circuit control unit  33  in the relay station  3 , the relay station  3  and the cordless extension master station  4  communicate with each other. Thereby, the wireless communication link is cut. Then, the process goes to step S 206 . In step S 206 , the relay station  3  cuts the wireless communication link with the doorphone master station  2 . In this case, by the control of the circuit control unit  33  in the relay station  3 , the relay station  3  and the doorphone master station  2  communicate with each other. Thereby, the wireless communication link is cut, which means that the wireless communication link is cut among the doorphone master station  2 , the relay station  3  and the cordless extension master station  4 . Afterward, the relay station  3  moves to the waiting state. When the above process ends, the process goes out of the flow. 
       FIG. 5  is a flow chart showing a process executed by the cordless extension master station  4 . The process is repeatedly executed. 
     First, in step S 301 , the cordless extension master station  4  determines whether or not it receives the call from the relay station  3 . Namely, the cordless extension master station  4  determines whether or not it receives the call signal from the relay station  3 . In the above process in step S 203  (see  FIG. 4 ), the relay station  3  transmits the call signal to the cordless extension master station  4 . When the cordless extension master station  4  receives the call from the relay station  3  (step S 301 ; Yes), the process goes to step S 302 . Meanwhile, when the cordless extension master station  4  does not receives the call from the relay station  3  (step S 301 ; No), the process returns to step S 301 . 
     In step S 302 , the cordless extension master station  4  determines whether or not the user pushes the talk button  46  in the cordless extension master station  4 . When the talk button  46  is pushed (step S 302 ; Yes), the process goes to step S 303 . Meanwhile, when the talk button  46  is not pushed (step S 302 ; No), the process returns to step S 302 . 
     In step S 303 , since the talk button  46  is pushed, the cordless extension master station  4  establishes the wireless communication link with the relay station  3 . Concretely, by the control of the circuit control unit  33  in the relay station  3 , the cordless extension master station  4  and the relay station  3  communicate with each other. Thereby, the wireless communication link is established. In this case, a talk start request signal is transmitted from the cordless extension master station  4  to the doorphone master station  2  via the relay station  3 . Thereby, the wireless communication link is established among the doorphone master station  2 , the relay station  3  and the cordless extension master station  4 . Namely, the sound link is formed among the doorphone entrance station  1 , the doorphone master station  2 , the relay station  3  and the cordless extension master station  4 . When the above process ends, the process goes to step S 304 . 
     In step S 304 , the cordless extension master station  4  determines whether or not the user pushes the end button  47 . When the end button  47  is pushed (step S 304 ; Yes), the process goes to step S 305 . Meanwhile, when the end button  47  is not pushed (step S 304 ; No), the process returns to step S 304 . 
     In step S 305 , since the end button  47  is pushed, the cordless extension master station  4  cuts the wireless communication link with the relay station  3 . In this case, by the control of the circuit control unit  33  in the relay station  3 , the cordless extension master station  4  and the relay station  3  communicate with each other. Thereby, the wireless communication link is cut. Afterward, the cordless extension master station  4  moves to the waiting state. When the above process ends, the process goes out of the flow. 
     As described above, each of the components of the doorphone system  101  executes the process, which can appropriately form the wireless communication link between the doorphone master station  2  and the cordless extension master station  4  via the relay station  3 . Thereby, it becomes possible to effectively enlarge the communicatable range between the doorphone master station  2  and the cordless extension master station  4 . 
     In the above embodiment, the relay station  3  capable of charging the cordless extension master station  4  is shown, but the present invention is not limited to this. Namely, it is unnecessary that the relay station  3  is formed as the charging device of the cordless extension master station  4 . Also, it is unnecessary that the relay station  3  is formed so that the ON/OFF state of the wireless communication function is switchable. Moreover, in the above embodiment, the doorphone system  101  including the single cordless extension master station  4  is shown, but the present invention is not limited to this. In another embodiment, the doorphone system can be formed with using two or more cordless extension master stations. 
       FIG. 6  is a schematic view showing a system configuration of a doorphone system  101   a  according to a modification of the first embodiment. The doorphone system  101   a  mainly includes the doorphone entrance station  1 , the doorphone master station  2 , a relay station  3   a  and three cordless extension master stations  4   a ,  4   b  and  4   c . The same reference numerals are given to the same components as those of the above doorphone system  101  (see  FIG. 1 ), and explanation thereof are omitted. 
     In the door phone system  101   a  according to the modification, the doorphone master station  2  and the relay station  3   a  are wirelessly connected, and the relay station  3   a  and the cordless extension master stations  4   a  to  4   c  are wirelessly connected. Concretely, in the doorphone system  101   a , the relay station  3   a  functions as a wireless master station, and the doorphone master station  2  and the cordless extension master stations  4   a  to  4   c  function as wireless extension master stations. Thereby, the wireless communication link is formed. Namely, the wireless communication link is established between the doorphone master station  2  and the cordless extension master stations  4   a  to  4   c  via the relay station  3 . Thereby, all the wireless communication between the doorphone master station  2  and the cordless extension master stations  4   a  to  4   c  is executed via the relay station  3   a.    
     Additionally, in the doorphone system  101   a , the relay station  3   a  is not formed as a device which can charge the cordless extension master stations  4   a  to  4   c , i.e., the relay station  3   a  does not have a function to charge the cordless extension master stations  4   a  to  4   c . Instead, the cordless extension master stations  4   a  to  4   c  are formed to be charged by charge mounts  5   a  to  5   c . In the above doorphone system  101   a , the wireless communication link is established by making the relay station  3   a  as a wireless master station. Therefore, by providing the relay station  3   a  at an appropriate position, it becomes possible to effectively enlarge the communicatable range between the doorphone master station  2  and the cordless extension master stations  4   a  to  4   c.    
     Second Embodiment 
     Next, a description will be given of a doorphone system according to a second embodiment of the present invention. The doorphone system according to the second embodiment is formed with using the cordless phone master station of the cordless phone instead of the relay station  3   a  and with using the cordless phone extension master station of the cordless phone instead of the cordless extension master stations  4   a  to  4   c . In this point, the doorphone system according to the second embodiment is different from the above doorphone system  101  according to the first embodiment. That is, the doorphone system according to the second embodiment is formed by the cordless phone master station having the same function (i.e., the function as a wireless master station) as that of the above relay station  3   a.    
       FIG. 7  is a schematic diagram showing a system configuration of a doorphone system  102  according to the second embodiment. The doorphone system  102  mainly includes the doorphone entrance station  1 , the doorphone master station  2 , the cordless phone master station  6  and the cordless phone extension master station  7 . The doorphone system  102  has two functions: a doorphone talking function for having a conversation with the visitor; and a phone talking function for phone talking via a telephone line. The same reference numerals are given to the same components as those of the above doorphone system  101  (see  FIG. 1 ), and explanations thereof are omitted. 
     The cordless phone master station  6  includes a microphone with which the user actually has a conversation and a handset unit  63  including a receiver, and it is formed to enable the phone talk via the telephone line. In addition, the cordless phone master station  6  and the doorphone master station  2  are wirelessly connected, and the cordless phone master station  6  and the cordless phone extension master station  7  are wirelessly connected. Concretely, in the door phone system  102 , the cordless phone master station  6  functions as a wireless master station, and the door phone master station  2  and the cordless phone extension master station  7  function as wireless extension master stations. Thereby, the wireless communication link is formed. Namely, via the cordless phone master station  6 , the wireless communication link between the doorphone master station  2  and the cordless phone extension master station  7  is established. Thereby, all of the wireless communication between the doorphone master station  2  and the cordless phone extension master station  7  is executed via the cordless phone master station  6 . 
     As mentioned above, in the second embodiment, the cordless phone master station  6  has the same function as that of the above relay station  3 . That is, in the second embodiment, the cordless phone master station  6  functions as a relay station for relaying the wireless communication between the doorphone master station  2  and the cordless phone extension master station  7  in the doorphone system  102 . The doorphone system  102  is formed in such a state that the communication protocol of the wireless unit  27  integrated with the doorphone master station  2  and the cordless phone extension master station  7  is implemented in conformity with (compatible with) a communication protocol of a normal cordless phone. 
       FIG. 8  is a block diagram showing the entire configuration of the doorphone system  102  according to the second embodiment. As described above, the doorphone system  102  includes the doorphone entrance station  1 , the doorphone master station  2 , the cordless phone master station  6  and the cordless phone extension master station  7 . The same reference numerals are given to the same components as those of the above-mentioned doorphone system  101  (see  FIG. 2 ), and explanations thereof are omitted. 
     The cordless phone master station  6  includes a wireless unit  61 , a sound signal processing unit  62 , a receiver  63   a , a microphone  63   b , a control unit  64 , a telephone line interface circuit  65 , an operation unit  66  and an antenna  67 . 
     The microphone  63   b  collects the sound of the user, and the receiver  63   a  outputs the sound. In this case, the microphone  63   b  and the receiver  63   a  form the handset unit  63 . The sound signal processing unit  62  executes the modulation/demodulation of the sound signal. A telephone line  69  is connected to the telephone line interface circuit  65 . Via the telephone line  69 , a sound of a conversation partner is received, and the sound of the user is transmitted. The operation unit  66  includes a ten-key (not shown), the talk button and the end button. In this case, the talk button in the operation unit  66  is pushed when the user performs the talk with using the cordless phone master station  6 , and the end button in the operation unit  66  is pushed when the user ends the talk with using the cordless phone master station  6 . The signal is inputted to the control unit  64  from the operation unit  66 , and the control unit  64  controls the wireless unit  61 , the sound signal processing unit  62  and the telephone line interface circuit  65 . 
     The wireless unit  61  can wirelessly communicate with the wireless unit  27  in the doorphone master station  2  and the wireless unit  71  in the cordless phone extension master station  7  via the antenna  67 . Concretely, the wireless unit  61  functions as a master station against the wireless units  27  and  71  (i.e., the wireless units  27  and  71  function as wireless extension master stations) to perform the wireless communication. Thereby, the wireless communication becomes possible between the doorphone master station  2  and the cordless phone extension master station  7  via the cordless phone master station  6 . In details, at the time of receiving the call signal from the doorphone master station  2 , the wireless unit  61  transmits the call signal to the cordless phone extension master station  7  via the antenna  67 . Thereby, the wireless communication link with the cordless phone extension master station  7  is established. In this manner, the wireless unit  61  corresponds to the second wireless unit. 
     The cordless phone extension master station  7  functions as the above cordless extension master station, and includes the wireless unit  71 , a sound signal processing unit  72 , a microphone  73 , a receiver  74 , a control unit  75 , an operation unit  76  and an antenna  77 . The microphone  73  collects the sound of the user, and the receiver  74  outputs the sounds of the visitor and the conversation partner. The operation unit  76  includes the ten-key (not shown), the talk button and the end button. In this case, the talk button in the operation unit  76  is pushed when the user performs the call with using the cordless phone extension master station  7 , and the end button in the operation unit  76  is pushed when the user ends the talk with using the cordless phone extension master station  7 . The sound signal processing unit  72  executes the modulation/demodulation of the sound signal. The signal is inputted to the control unit  75  from the operation unit  76 , and the control unit  75  controls the sound signal processing unit  72  and the wireless unit  71 . 
     The wireless unit  71  can wirelessly communicate with the cordless phone master station  6  via the antenna  77 . Concretely, the wireless unit  71  functions as an extension master station against the wireless unit  61  in the cordless phone master station  6  (i.e., the wireless unit  61  functions as a master station), and executes the wireless communication. In details, the wireless unit  71  receives the call signal from the cordless phone master station  6 , and establishes the wireless communication link with the cordless phone master station  6  in such a case that the talk button in the operation unit  76  is pushed. Thereby, the wireless communication link is established among the doorphone master station  2 , the cordless phone master station  6  and the cordless phone extension master station  7 . Namely, the sound link is formed among the doorphone entrance station  1 , the doorphone master station  2 , the cordless phone master station  6  and the cordless phone extension master station  7 . Thereby, it becomes possible that the visitor and the user have a conversation between the doorphone entrance station  1  and the cordless phone extension master station  7 . As described above, the wireless unit  71  corresponds to the third wireless unit. 
     Now, the doorphone system  102  according to the above second embodiment is compared with a system (hereinafter referred to as “doorphone system according to a second comparative example”) formed by combining the cordless phone and the doorphone system simultaneously including two wireless master stations, i.e., the doorphone master station and the cordless phone master station/extension master station. In the doorphone system according to the second comparative example, it is necessary to implement the special protocol to all of the doorphone master station, the doorphone entrance station, the cordless phone master station and the cordless phone extension master station in order to realize mutual communication among the two wireless master stations, the doorphone entrance station and the cordless phone extension master station. Therefore, the system becomes complicated, which increases the cost. On the other hand, in the doorphone system  102  according to the second embodiment, the doorphone master station  2  functions as a wireless extension master station, and the cordless phone master station  6  functions as a wireless master station. Thereby, the wireless communication link is established. Therefore, the system can be easily formed by combining the doorphone system and the cordless phone. 
     Next, a description will be given of the process executed in the doorphone system  102 , with reference to  FIG. 9  to  FIG. 11 . 
       FIG. 9  is a flow chart showing the process executed by the doorphone entrance station  1  and the doorphone master station  2 . In  FIG. 9 , the main body (the doorphone entrance station  1  or the doorphone master station  2 ) which executes the process in each step is shown in a parenthesis. Additionally, the process is repeatedly executed. 
     First, in step S 401 , the doorphone entrance station  1  determines whether or not the visitor pushes the call button  13 . When the call button  13  is pushed (step S 401 ; Yes), the process goes to step S 402 . When the call button  13  is not pushed (step S 401 ; No), the process returns to step S 401 . 
     In step S 402 , since the call button  13  of the doorphone entrance station  1  is pushed, the doorphone master station  2  executes the process for calling the cordless phone master station  6 . Concretely, the doorphone master station  2  transmits the call signal to the cordless phone master station  6 . Then, the process goes to step S 403 . In step S 403 , the doorphone master station  2  establishes the wireless communication link with the cordless phone master station  6 . Concretely, by the control of the control unit  64 , the doorphone master station  2  and the cordless phone master station  6  communicate with each other. Thereby, the wireless communication link is established. Then, the process goes to step S 404 . 
     In step S 404 , the doorphone master station  2  cuts the wireless communication link with the cordless phone master station  6 . Concretely, when the user pushes the end button in the cordless phone extension master station  7  and the wireless communication link between the cordless phone master station  6  and the cordless phone extension master station  7  is cut, the doorphone master station  2  releases the wireless communication link with the cordless phone master station  6 . In this case, by the control of the control unit  64 , the doorphone master station  2  and the cordless phone master station  6  communicate with each other. Thereby, the wireless communication link is cut. Afterward, the doorphone master station  2  moves to the waiting state. When the above process ends, the process goes out of the flow. 
       FIG. 10  is a flow chart showing the process executed by the cordless phone master station  6 . The process is repeatedly executed. 
     First, in step S 501 , the cordless phone master station  6  determines whether or not it receives the call from the doorphone master station  2 . Namely, the cordless phone master station  6  determines whether or not it receives the call signal from the doorphone master station  2 . The doorphone master station  2  transmits the call signal to the cordless phone master station  6  in the above process in step S 402  (see  FIG. 9 ). When the cordless phone master station  6  receives the call from the doorphone master station  2  (step S 501 ; Yes), the process goes to step S 502 . Meanwhile, when the cordless phone master station  6  does not receive the call (step S 501 ; No), the process returns to step S 501 . 
     In step S 502 ; since the cordless phone master station  6  receives the call from the doorphone master station  2 , the cordless phone master station  6  establishes the wireless communication link with the doorphone master station  2 . Concretely, the doorphone master station  2  and the cordless phone master station  6  communicate with each other. Thereby, the wireless communication link is established. Then, the process goes to step S 503 . In step S 503 , the cordless phone master station  6  executes a process for calling the cordless phone extension master station  7 . Concretely, the cordless phone master station  6  transmits the call signal to the cordless phone extension master station  7 . Then, the process goes to step S 504 . 
     In step S 504 , the cordless phone master station  6  establishes the wireless communication link with the cordless phone extension master station  7 . Concretely, by the control of the control unit  64 , the cordless phone master station  6  and the cordless phone extension master station  7  communicate with each other. Thereby, the wireless communication link is established. Then, the process goes to step S 505 . 
     In step S 505 , the cordless phone master station  6  cuts the wireless communication link with the cordless phone extension master station  7 . Concretely, when the user pushes the end button in the cordless phone extension master station  7 , the cordless Phone master station  6  releases the wireless communication link with the cordless phone extension master station  7 . In this case, by the control of the control unit  64 , the cordless phone master station  6  and the cordless phone extension master station  7  communicate with each other. Thereby, the wireless communication link is cut. Then, the process goes to step S 506 . In step S 506 , the cordless phone master station  6  cuts the wireless communication link with the doorphone master station  2 . In this case, by the control of the control unit  64 , the cordless phone master station  6  and the doorphone master station  2  communicate with each other. Thereby, the wireless communication link is cut. Therefore, the wireless communication link among the doorphone master station  2 , the cordless phone master station  6  and the cordless phone extension master station  7  is cut. Afterward, the cordless phone master station  6  moves to the waiting state. When the above process ends, the process goes out of the flow. 
       FIG. 11  is a Flow chart showing the process executed by the cordless phone extension master station  7 . The process is repeatedly executed. 
     First, in step S 601 , the cordless phone extension master station  7  determines whether or not it receives the call from the cordless phone master station  6 . Namely, the cordless phone extension master station  7  determines whether or not it receives the call signal from the cordless phone master station  6 . In the above process in step S 503  (see  FIG. 10 ), the cordless phone master station  6  transmits the call signal to the cordless phone extension master station  7 . When the cordless phone extension master station  7  receives the call from the cordless phone master station  6  (step S 601 ; Yes), the process goes to step S 602 . Meanwhile, when the cordless phone extension master station  7  does not receive the call (step S 601 ; No), the process returns to step S 601 . 
     In step S 602 , the cordless phone extension master station  7  determines whether or not the user pushes the talk button in the cordless phone extension master station  7 . When the talk button is pushed (step S 602 ; Yes), the process goes to step S 603 . Meanwhile, when the talk button is not pushed (step S 602 ; No), the process returns to step S 602 . 
     In step S 603 , since the talk button is pushed, the cordless phone extension master station  7  establishes the wireless communication link with the cordless phone master station  6 . Concretely, by the control of the control unit  64 , the cordless phone extension master station  7  and the cordless phone master station  6  communicate with each other. Thereby, the wireless communication link is established. In this case, the talk start request signal is transmitted to the doorphone master station  2  from the cordless phone extension master station  7  via the cordless phone master station  6 . Thereby, the wireless communication link is established among the doorphone master station  2 , the cordless phone master station  6  and the cordless phone extension master station  7 . Namely, the sound link is formed among the doorphone entrance station  1 , the doorphone master station  2 , the cordless phone master station  6  and the cordless phone extension master station  7 . When the above process ends, the process returns to step S 604 . 
     In step S 604 , the cordless phone extension master station  7  determines whether or not the user pushes the end button. When the end button is pushed (step S 604 ; Yes), the process goes to step S 605 . Meanwhile, when the end button is not pushed (step S 604 ; No), the process goes to step S 604 . 
     In step S 605 , since the end button is pushed, the cordless phone extension master station  7  cuts the wireless communication link with the cordless phone master station  6 . In this case, by the control of the control unit  64 , the cordless phone extension master station  7  and the cordless phone master station  6  communicate with each other. Thereby, the wireless communication link is cut. Afterward, the cordless phone extension master station  7  moves to the waiting state. When the above process ends, the process goes out of the flow. 
     As described above, each of the components of the doorphone system  102  executes the process. Thereby, the wireless communication link can be appropriately formed between the doorphone master station  2  and the cordless phone extension master station  7  via the cordless phone master station  6 . 
     In the above embodiment, such an example that the doorphone system  102  is formed with using the cordless phone master station  6  instead of the relay station  3  is shown. However, as another example, a new doorphone system can be formed by adding the cordless phone master station  6  to the doorphone system  101  (see  FIG. 1 ) including the relay station  3 . In this case, the wireless communication function in the relay station  3  is made in the OFF state (in an invalid state), which makes the relay station  3  function only as the charge mount of the cordless extension master station  4 . The master-sub relationship among the doorphone master station  2 , the cordless extension master station  4  and the cordless phone master station  6  is reregistered. Thereby, a new system can be formed. Namely, the cordless phone master station  6  functions as a wireless master station, and the doorphone master station  2  and the cordless extension master a station  4  function as wireless extension master stations. Thereby, the new wireless communication link is formed. In still another example, by adding the cordless phone master station  6  to the doorphone system  101   a  (see  FIG. 6 ), a new system can be formed. Further, by adding not only the cordless phone master station  6  but also the cordless phone extension master station  7  to the doorphone system  101  or  101   a , a new system can be formed, too. 
     Modification 
     In the above embodiments, the doorphone systems  101 ,  101   a  and  102  with using only the sound signal are shown. However, the present invention can be applied to the doorphone system capable of communicating not only the sound signal but also a picture signal photographed by a camera. Namely, the present invention is applicable to a television doorphone, too. Furthermore, the present invention is applicable to a room (baby) monitoring system, a security (monitor) camera system and a system including a recorder in the systems. 
     Additionally, in  FIG. 8 , the cordless phone master station  6  includes the wireless unit  61 , the sound signal processing unit  62 , the receiver  63   a , the microphone  63   b , the control unit  64 , the telephone line interface circuit  65 , the operation unit  66  and the antenna  67 . However, it is not limited that the cordless phone master station  6  is formed in this manner. In another example, the cordless phone master station can be formed only by the wireless unit, the control unit, the telephone line interface circuit and the antenna. In this case, it is preferable that the phone function of the cordless phone extension master station is used. Moreover, when the cordless phone master station is formed in this method, it is also preferable that the cordless phone master station functions as the charge mount of the cordless phone extension master station. 
     As described above, the doorphone system according to this embodiment includes the doorphone entrance station, the doorphone master station connected to the doorphone entrance station via a wire, the relay station wirelessly connected to the doorphone master station and the cordless extension master station wirelessly connected to the relay station, and the wireless communication link between the doorphone master station and the cordless extension master station is established via the relay station. Thereby, it becomes possible to effectively enlarge the communicatable range between the doorphone master station and the cordless extension master station. 
     The invention may be embodied on other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning an range of equivalency of the claims are therefore intended to embraced therein. 
     The entire disclosure of Japanese Patent Application No. 2007-243700 filed on Sep. 20, 2007 including the specification, claims, drawings and summary is incorporated herein by reference in its entirety.