Abstract:
Provided is a technique of reducing time and labor of replacing and charging the battery. This invention provides an electronic apparatus, which has a name written on a front side thereof, including: a radio communication apparatus; a secondary battery; a solar battery on the front side; and a display unit on a backside thereof, in which the solar battery is installed to be tilted to make a distance between an upper side thereof and the display unit smaller than a distance between a lower side thereof and the display unit.

Description:
CLAIM OF PRIORITY  
       [0001]     The present application claims priority from Japanese patent application P2005-201434 filed on Jul. 11, 2005, the content of which is hereby incorporated by reference into this application.  
       BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to an electronic apparatus for performing radio communication, and more particularly to an electronic apparatus which can be carried by a person.  
         [0003]     Developments of a sensor network system constituted of a sensor node and a server have been proceeding in recent years. The sensor node is carried by a person or the like and measures a state or the like (sensor data) of the person. The sensor node then transmits the measured sensor data to the server. The server executes various processes based on the received sensor data.  
         [0004]     The conventional sensor node includes a primary or secondary battery as a power source.  
         [0005]     However, the primary battery has had a problem in that it must be replaced. The secondary battery has had a problem in that it must be recharged.  
         [0006]     A node that solves the problems is disclosed in JP 08-223067 A. The node includes a solar battery and a secondary battery, and the secondary battery is recharged with power generated by the solar battery.  
       SUMMARY OF THE INVENTION  
       [0007]     In the case of the conventional node, however, the power generated by the solar battery is too weak to supply sufficient power to the secondary battery. Thus, the secondary battery must be externally charged even when the conventional node includes the solar battery.  
         [0008]     This invention has been made in view of the foregoing problems, and has an object to provide a node in which there is no need to replace and recharge a battery.  
         [0009]     This invention provides an electronic apparatus, which has a name written on a front side thereof, including: a radio communication apparatus; a secondary battery; a solar battery on the front side; and a display unit on a backside thereof, in which the solar battery is installed to be tilted to make a distance between an upper side thereof and the display unit smaller than a distance between a lower side thereof and the display unit.  
         [0010]     According to an embodiment of this invention, there is no need to replace and recharge the battery. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The present invention can be appreciated by the description which follows in conjunction with the following figures, wherein:  
         [0012]      FIG. 1  is a block diagram of a sensor network system according to a first embodiment of this invention;  
         [0013]      FIG. 2  is a block diagram of a name tag type node according to the first embodiment of this invention;  
         [0014]      FIG. 3A  is a front diagram of the name tag type node according to the first embodiment of this invention;  
         [0015]      FIG. 3B  is a back diagram of the name tag type node according to the first embodiment of this invention;  
         [0016]      FIG. 4  is a side diagram of the name tag type node according to the first embodiment of this invention;  
         [0017]      FIG. 5  is a side diagram of the name tag type node according to the first embodiment of this invention;  
         [0018]      FIG. 6  is an explanatory diagram of the name tag type node according to the first embodiment of this invention;  
         [0019]      FIG. 7  is an explanatory diagram of power of the name tag type node according to the first embodiment of this invention;  
         [0020]      FIG. 8  is an explanatory diagram of power of the name tag type node according to the first embodiment of this invention;  
         [0021]      FIG. 9  is a block diagram of an event action control unit of a server according to the first embodiment of this invention;  
         [0022]      FIG. 10  is a diagram showing a composition of an event action table according to the first embodiment of this invention;  
         [0023]      FIG. 11  is a sequential diagram of a message transmission/reception process of the sensor network system according to the first embodiment of this invention;  
         [0024]      FIG. 12  is a sequential diagram of a message transmission/reception process of the name tag type node according to the first embodiment of this invention;  
         [0025]      FIG. 13  is a sequential diagram of a message transmission/reception process to be performed between name tag type nodes according to the first embodiment of this invention;  
         [0026]      FIG. 14  is a block diagram of a sensor network system according to a second embodiment of this invention;  
         [0027]      FIG. 15  is an explanatory diagram of how the sensor network system of the second embodiment of this invention is installed; and  
         [0028]      FIG. 16  is a sequential diagram of a position detection process of the sensor network system according to the second embodiment of this invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]     The preferred embodiments of this invention will be described with reference to the accompanying drawings.  
       First Embodiment  
       [0030]      FIG. 1  is a block diagram of a sensor network system according to a first embodiment of this invention.  
         [0031]     The sensor network system includes a name tag type node  100 , a server  200 , a base station  300 , and a network  600 .  
         [0032]     As described below referring to FIGS.  2  to  6 , the name tag type node  100  is an electronic apparatus which communicates with the server  200  through the base station  300 . The name tag type node  100  functions as a name tag by having a name or the like written on its front side. For example, a person carries the name tag type node  100  by dangling it from a neck, or by attaching it to clothes by a clip or the like. The name tag type node  100  is carried to be used in an exhibition hall, a lecture hall, a company, a hospital, public facilities, or the like.  
         [0033]     The network  600  interconnects the server  200  and the base station  300 .  
         [0034]     The base station  300  communicates with the name tag type node  100  by radio. The base station  300  transfers data received from the name tag type node  100  to the server  200 . Similarly, the base station  300  transfers data received from the server  200  to the name tag type node  100 .  
         [0035]     The name tag type node  100  may include a function of the base station  300 . In this case, the name tag type node  100  transfers data received from another name tag type node  100  to the server  200 .  
         [0036]     The server  200  is a computer which includes an event action control unit described below with reference to  FIG. 9 .  
         [0037]      FIG. 2  is a block diagram of the name tag type node  100  according to the first embodiment of this invention.  
         [0038]     The name tag type node  100  includes a solar battery  102 , a secondary battery  112 , a charging terminal  115 , a power source board  113 , an RF board  105 , a microcomputer  116 , a sensor  117 , and an antenna  106 .  
         [0039]     The solar battery  102  generates power by taking out power from sunlight. It should be noted that the name tag type node  100  may include, in place of the solar battery  102 , a generator for generating power by using another method.  
         [0040]     The secondary battery  112  supplies power to the name tag type node  100 . The secondary battery  112  has ratings in current and voltage for charging. Also, the secondary battery  112  has ratings in current and voltage for discharging. For example, the secondary battery  112  is a lithium-ion battery. The lithium-ion battery is best suited to the secondary battery  112 , because it has a large capacity per unit volume, and is not affected by a memory effect during charging.  
         [0041]     The charging terminal  115  charges the secondary battery  112  when it is connected to an external power source.  
         [0042]     The power source board  113  includes a diode  118 , an overcharge prevention circuit  119 , an overdischarge prevention circuit  120 , a regulator  121 , and a voltage dividing circuit  122 .  
         [0043]     The diode  118  is a semiconductor which supplies a current only in one direction.  
         [0044]     The overcharge prevention circuit  119  prevents overcharge of the secondary battery  112 . The overdischarge prevention circuit  120  prevents overdischarge of the secondary battery  112 .  
         [0045]     The regulator  121  makes constant a voltage supplied to the RF board  105 , the microcomputer  116 , and the sensor  117 .  
         [0046]     The voltage dividing circuit  122  sets a voltage of the solar battery  102  and a voltage of the secondary battery  112  to a constant ratio. Specifically, the voltage dividing circuit  122  sets the voltage of the solar battery  102  or the voltage of the secondary battery  112  to a voltage that can be measured by the microcomputer  116 .  
         [0047]     The RF board  105  has a circuit for radio communication mounted thereon. The RF board  105  communicates with the base station  300  through the antenna  106  by radio.  
         [0048]     The microcomputer  116  controls the entire name tag type node  100 . For example, the microcomputer  116  measures the voltage of the secondary battery  112 . Then, it estimates a charging period of the secondary battery based on the measured voltage of the secondary battery  112 .  
         [0049]     The microcomputer  116  measures the voltage of the solar battery  102 . Then, it obtains illuminance around the name tag type node  100  based on the measured voltage of the solar battery  102 . When the obtained illuminance is low, the microcomputer  116  may control the name tag type node  100  to reduce power consumption.  
         [0050]     The microcomputer  116  may be started at a predetermined cycle and set in a sleep state in other cases to thereby reduce power consumption of the microcomputer  116 .  
         [0051]     The sensor  117  obtains various pieces of information on a temperature, humidity, and acceleration.  
         [0052]     Next, a power flow of the name tag type node  100  will be described.  
         [0053]     Power generated by the solar battery  102  flows through the diode  118  and the overcharge prevention circuit  119  to charge the secondary battery  112 .  
         [0054]     The power charged to the secondary battery  112  flows through the diode  118 , the overdischarge prevention circuit  120 , and the regulator  121  to be supplied to the RF board  105 , the microcomputer  116 , and the sensor  117 .  
         [0055]     The voltage of the solar battery  102  may be set higher than that of the secondary battery  112  to thereby permit the solar battery  102  to directly supply the power to the RF board  105 , the microcomputer  116 , and the sensor  117 .  
         [0056]     In other words, the solar battery  102  provided to the name tag type node  100  of this embodiment eliminates the need to replace and recharge the battery. This is particularly effective for the sensor network system which includes many name tag type nodes  100 .  
         [0057]      FIG. 3A  is a front diagram of the name tag type node  100  according to the first embodiment of this invention.  
         [0058]     The solar battery  102 , the LED  103 , the RF board  105 , and the antenna  106  are installed on a front side of the name tag type node  100 .  
         [0059]     The LED  103  emits a light when predetermined conditions are satisfied. For example, the LED  103  emits a light when the name tag type node  100  receives information from the server  200  to thereby notify the reception of the information to the user.  
         [0060]     The solar battery  102 , the LED  103 , the antenna  106 , and the name tag type node  100  shown in the block diagram of  FIG. 2  have been described, and thus description thereof will be omitted.  
         [0061]     The antenna  106  is installed in a position far from the solar battery  102  and the LCD  107 . Especially, the antenna  106  is disposed not to overlap the solar battery  102  or the LCD  107  when viewed from the front. This is because the solar battery  102  and the LCD  107  obstruct communication performed through the antenna  106 .  
         [0062]      FIG. 3B  is a back diagram of the name tag type node  100  according to the first embodiment of this invention.  
         [0063]     The LCD  107 , an operation switch  108 , a reset switch  110 , a buzzer  111 , a secondary battery  112 , the power source board  113 , a power supply switch  114 , the charging terminal  115 , the microcomputer  116 , and the sensor  117  are installed in a backside of the name tag type node  100 .  
         [0064]     The LCD  107  is a liquid crystal display for displaying various pieces of information. The name tag type node  100  may include another type of display in place of the LCD  107 .  
         [0065]     The operation switch  108  is operated by the user. The user operates the operation switch  108  to input various pieces of information to the name tag type node  100 . The user operates the operation switch  108  to select displaying or nondisplaying of the LCD  107 . Thus, it is possible to reduce power consumption of the LCD  107 .  
         [0066]     The reset switch  110  resets the name tag type node  100  when it is operated by the user.  
         [0067]     The buzzer  111  emits a sound when predetermined conditions are satisfied. For example, the buzzer  111  emits a sound when the name tag type node  100  receives information from the server  200 . Accordingly, the buzzer  111  can notify the reception of the information to the user.  
         [0068]     The power supply switch  114  switches between power ON and OFF of the name tag type node  100 .  
         [0069]     The secondary battery  112 , the power source board  113 , the charging terminal  115 , the microcomputer  116 , and the sensor  117  shown in the bock diagram of  FIG. 2  of the name tag type node  100  have been described, and thus description thereof will be omitted.  
         [0070]     The name tag type node  100  can have the solar battery  102  of a large area on its front side by including the LCD  107 , the operation switch  108 , and the like on its backside. Hence, it is possible to increase a power generation amount of the solar battery  102 .  
         [0071]      FIG. 4  is a side diagram of the name tag type node  100  according to the first embodiment of this invention.  
         [0072]     The solar battery  102  is installed to be tilted upward. Specifically, the solar battery  102  is disposed to be tilted such that a distance between its upper side and the LCD  107  is made smaller than that between its lower side and the LCD  107 . Accordingly, the solar battery  102  can obtain light more efficiently to generate large power. For example, a solar battery  102  installed to be tilted by an angle of 5° with respect to the LCD  107  can generate power larger by 30 to 40% than that of a solar battery installed in parallel with the LCD  107 .  
         [0073]     The name tag type node  100  is made thinner at its upper portion than at its bottom portion. Accordingly, the name tag type node  100  does not bring any discomfort to the user even when the name tag type node  100  includes the solar battery tilted upward.  
         [0074]     The secondary battery  112  is installed lower than a center of the name tag type node  100  or the solar battery  102 . The upper portion of the name tag type node  100  can be made thinner by including the thick secondary battery  112  in its lower portion.  
         [0075]     The name tag type node  100  may take a form shown in  FIG. 5 .  
         [0076]      FIG. 5  is a side diagram of the name tag type node  100  according to the first embodiment of this invention.  
         [0077]     Different from the name tag type node  100  of  FIG. 4 , the name tag type node  100  of this explanatory diagram has uniform thickness. Other components are similar to those of the name tag type node of  FIG. 4 , and thus description thereof will be omitted.  
         [0078]     In other words, irrespective of the thickness of the name tag type node  100 , the solar battery  102  can generate large power by being installed to be tilted upward.  
         [0079]      FIG. 6  is an explanatory diagram of the name tag type node  100  according to the first embodiment of this invention.  
         [0080]     A transparent film  140  is installed at the front of the solar battery  102 . Information containing a division to which a user belongs, a user name, and the like is written on the transparent film  140 . Thus, the name tag type node  100  functions as a name tag. The name tag type node  100  can include a solar battery  102  of a large area by having the transparent film  140 , on which the information is written, placed at the front of the solar battery  102 .  
         [0081]     A front portion other than a portion corresponding to the solar battery  102  does not need to be transparent. For example, a company logo  130  or the like is written on the front portion other than the portion corresponding to the solar battery  102 .  
         [0082]      FIG. 7  is an explanatory diagram of power of the name tag type node  100  according to the first embodiment of this invention.  
         [0083]     This explanatory diagram shows a case where a power generation amount of the solar battery  102  exceeds a power consumption amount of the name tag type node  100 .  
         [0084]     The explanatory diagram includes a graph regarding a power generation amount of the solar battery  102 , a power consumption amount of the name tag type node  100 , and a voltage of the secondary battery  112 . An abscissa of each of these graphs indicates time.  
         [0085]     As shown in the explanatory diagram, the power generation amount of the solar battery  102  greatly changes depending on time. On the other hand, the name tag type node  100  operates at a predetermined interval to consume power at a predetermined interval.  
         [0086]     As shown in the explanatory diagram, the power generation amount of the solar battery  102  exceeds the power consumption amount of the name tag type node  100 . Thus, a voltage of the secondary battery  112  is substantially maintained constant. In this case, the name tag type node  100  does not need any charging from outside.  
         [0087]      FIG. 8  is an explanatory diagram of power of the name tag type node  100  according to the first embodiment of this invention.  
         [0088]     This explanatory diagram shows a case where a power generation amount of the solar battery  102  is smaller than a power consumption amount of the name tag type node  100 .  
         [0089]     The explanatory diagram includes a graph regarding a power generation amount of the solar battery  102 , a power consumption amount of the name tag type node  100 , and a voltage of the secondary battery  112 . An abscissa of each of these graphs indicates time.  
         [0090]     As shown in the explanatory diagram, the power generation amount of the solar battery  102  is smaller than the power consumption amount of the name tag type node  100 . Thus, a voltage of the secondary battery  112  gradually decreases. In this case, the name tag type node  100  needs to be externally charged.  
         [0091]      FIG. 9  is a block diagram of an event action control unit  201  of the server  200  according to the first embodiment of this invention.  
         [0092]     The event action control unit  201  includes an event action registration interface  202 , an action execution unit  203 , an event condition judgment unit  204 , a sensing data detection unit  205 , an event action retrieval section  206 , and an event action table  210 .  
         [0093]     First, the event action table  210  will be described.  
         [0094]      FIG. 10  is a diagram showing a composition of the event action table  210  according to the first embodiment of this invention.  
         [0095]     The event action table  210  contains a node ID  2101 , event contents  2102 , a condition  2103 , and an action  2104 .  
         [0096]     The node ID  2101  is a unique identifier of the name tag type node  100 .  
         [0097]     The event contents  2102  and the condition  2103  are requirements for generating an event of a corresponding record.  
         [0098]     The event contents  2102  are types of sensor data received by the event action control unit  201 . For example, inquiry/reply reception (for a record  2105 ), position information reception (for a record  2106 ), or the like is stored in the event contents  2102 .  
         [0099]     The condition  2103  is for relating sensor data received by the event action control unit  201  to a corresponding record. Destination address information of the sensor data (for the record  2105 ), position information of the name tag type node  100  which has transmitted the sensor data (for the record  2106 ), or the like is stored in the conditions  2103 . Other conditions such as measuring time of the sensor data and a changing amount of the sensor data may be stored as the condition  2103 .  
         [0100]     The action  2104  indicates processing contents at an occurrence of an event. For example, the action  2104  may be message transfer processing (for the record  2105 ), or warning message transmission processing (for the record  2106 ). The message transfer processing shown in  FIG. 13  will be described below. Other processing contents may be stored as the action  2104 .  
         [0101]     Now, referring back to  FIG. 9 , description will be made.  
         [0102]     When updating contents of the event action table  210 , a management user inputs an event updating request through the user interface. It should be noted that the event updating request is for registering, changing, or deleting records in the event action table  210 .  
         [0103]     The input event updating request is sent though the user interface to the event action registration interface  202 . The event action registration interface  202  updates the event action table  210  based on the received event updating request.  
         [0104]     The sensing data detection unit  205  receives information (sensor data) obtained by the name tag type node  100  from the base station  300 , and sends the information to the event action retrieval unit  206 .  
         [0105]     The event action retrieval unit  206  determines a name tag type node  100  which has transmitted the sensor data. Next, the event action retrieval unit  206  judges whether a record having a node ID  2101  that corresponds to an identifier of the determined name tag type node  100  exists in the event action table  210 . Accordingly, judgment is made as to whether an event regarding the name tag type node  100  exists in the event action table  210 . If the event exists in the event action table  210 , the received sensor data is sent to the event condition judgment unit  204 .  
         [0106]     The event condition judgment unit  204  judges whether the received sensor data satisfies the event contents  2102  and the conditions  2103  in the event action table  210  or not. If the event contents  2102  and the conditions  2103  are satisfied, an action  2104  is extracted from a record which satisfies these conditions. Then, the extracted action  2104  is notified to the action execution unit  203 .  
         [0107]     The action execution unit  203  executes the notified action  2104 .  
         [0108]     As described above, the event action control unit  201  executes processing corresponding to the received sensor data. The event action control unit  201  executes various processing operations, whereby diverse ubiquitous applications can be realized.  
         [0109]     Next, description will be made of a process when the name tag type node  100  is used as a communication tool.  
         [0110]      FIG. 11  is a sequential diagram of a message transmission/reception process of the sensor network system according to the first embodiment of this invention.  
         [0111]     The management user inputs a message for the user of the name tag type node  100  to the server  200 . The management user may also select a message to be transmitted to the name tag type node  100  from among the messages preregistered in the server  200 . In this case, the message is an inquiry message to the user of the name tag type node  100 .  
         [0112]     The server  200  generates an inquiry message based on information input from the management user ( 511 ). At this time, the server  200  includes a node ID of a name tag type node  100  to which the massage is to be transmitted in the inquiry message to designate a destination address of the inquiry message.  
         [0113]     Next, the server  200  transmits the generated inquiry message to the base station  300  at predetermined timing ( 512 ). The predetermined timing includes a time point when a transmission request is received from the user, when fixed time expires, or when a condition event occurs.  
         [0114]     Then, the base station  300  receives the inquiry message from the server  200 . The base station  300  holds the received inquiry message.  
         [0115]     On the other hand, the name tag type node  100  starts the microcomputer  116  at a predetermined cycle ( 513 ). It should be noted that the name tag type node  100  also starts the microcomputer  116  when information is input from the user.  
         [0116]     Next, the name tag type node  100  obtains (senses) various pieces of information by using the sensor  117  ( 514 ).  
         [0117]     Subsequently, the name tag type node  100  makes an inquiry by radio to the base station  300  about whether the base station  300  holds the message addressed to the name tag type node  100  ( 515 ).  
         [0118]     Upon reception of the inquiry from the name tag type node  100 , the base station  300  judges whether it holds a message addressed to the name tag type node  100  or not.  
         [0119]     If it is judged that the message addressed to the name tag type node  100  is not held, the base station  300  informs the name tag type node  100  to that effect.  
         [0120]     On the other hand, if it is judged that the message addressed to the name tag type node  100  is held, the base station  300  transmits the message to the name tag type node  100 .  
         [0121]     Then, the name tag type node  100  receives the inquiry message from the base station  300  ( 516 ).  
         [0122]     Upon reception of the inquiry message, the name tag type node  100  lights the LED  103  for a fixed time, and sounds the buzzer  111  for a fixed time simultaneously ( 517 ). Accordingly, the name tag type node  100  notifies the reception of the message to the user.  
         [0123]     Next, the name tag type node  100  displays the received inquiry message on the LCD  107 .  
         [0124]     The user inputs a reply for the displayed inquiry message to the name tag type node  100 . The user may also select a reply message to be returned to the server  200  from among the reply messages preregistered in the name tag type node  100 .  
         [0125]     The name tag type node  100  generates a reply message based on the information input from the user. Then, the generated reply message is transmitted to the base station  300  ( 519 ).  
         [0126]     Next, the name tag type node  100  turns OFF the displaying on the LCD  107  ( 521 ). The name tag type node  100  sets the microcomputer  116  in a sleep state ( 522 ).  
         [0127]     Meanwhile, the base station  300  receives the reply message from the name tag type node  100 , and transfers the received reply message to the server  200 .  
         [0128]     The server  200  receives the reply message from the base station  300  ( 520 ).  
         [0129]     As described above, the server  200  receives the reply message to the inquiry message from the name tag type node  100 .  
         [0130]      FIG. 12  is a sequential diagram of a message transmission process of the name tag type node  100  according to the first embodiment of this invention.  
         [0131]     The name tag type node  100  starts the microcomputer  116  at a predetermined cycle ( 501 ). It should be noted that the name tag type node  100  also starts the microcomputer  116  when information is input from the user.  
         [0132]     Next, the name tag type node  100  turns ON displaying on the LCD  107  ( 502 ). The name tag type node  100  obtains (senses) various pieces of information by using the sensor  117  ( 503 ).  
         [0133]     The user inputs a message for the management user to the name tag type node  100 . In this case, the user inputs an inquiry to the management user. The user may also select an inquiry message to be transmitted to the server  200  from among the inquiry messages preregistered in the name tag type node  100 .  
         [0134]     The name tag type node  100  generates an inquiry message based on the information input from the user ( 504 ). Then, the name tag type node  100  transmits the generated inquiry message to the base station  300  ( 505 ).  
         [0135]     Next, the name tag type node  100  turns OFF the displaying on the LCD  107  ( 507 ).  
         [0136]     The name tag type node  100  sets the microcomputer  116  in a sleep state ( 508 ).  
         [0137]     Meanwhile, the base station  300  receives the inquiry message from the name tag type node  100 , and transfers the received inquiry message to the server  200 .  
         [0138]     The server  200  receives the inquiry message from the base station  300  ( 506 ).  
         [0139]     As described above, the name tag type node  100  transmits the message to the server  200 .  
         [0140]      FIG. 13  is a sequential diagram of a message transmission/reception process to be performed between the name tag type nodes  100  according to the first embodiment of this invention.  
         [0141]     This explanatory diagram shows a case where an inquiry is transmitted from a name tag type node A  100  to a name tag type node B  100 .  
         [0142]     The name tag type node A  100  starts the microcomputer  116  at a predetermined cycle ( 531 ). It should be noted that the name tag type node A  100  also starts the microcomputer  116  when information is input from the user.  
         [0143]     Next, the name tag type node A  100  turns ON displaying on the LCD  107  ( 532 ). The name tag type node A  100  obtains (senses) various pieces of information by using the sensor  117  ( 533 ).  
         [0144]     The user inputs an inquiry for a user of the name tag type node B  100  to the name tag type node A  100 . The user may also select an inquiry message to be transmitted to the name tag type node B  100  from among the inquiry messages preregistered in the name tag type node A  100 .  
         [0145]     The name tag type node A  100  generates an inquiry message based on the information input from the user ( 534 ). Then, the name tag type node A  100  transmits the generated inquiry message to the base station  300  ( 535 ).  
         [0146]     Next, the name tag type node  100  A turns OFF the displaying on the LCD  107  ( 536 ). The name tag type node A  100  sets the microcomputer  116  in a sleep state ( 537 ).  
         [0147]     Meanwhile, the base station  300  receives the inquiry message from the name tag type node A  100 , and transfers the received inquiry message to the server  200 .  
         [0148]     The server  200  receives the inquiry message from the base station  300 , and determines a destination address of the received inquiry message. In this case, it is determined that the destination address of the inquiry message is the name tag type node B  100 . A base station  300  that communicates with the judged name tag type node B  100  is retrieved ( 538 ).  
         [0149]     Subsequently, the inquiry message is transferred to the retrieved base station  300  ( 539 ).  
         [0150]     Then, the base station  300  receives the inquiry message from the server  200 . The base station  300  holds the received inquiry message.  
         [0151]     Meanwhile, the name tag type node B  100  starts the microcomputer  116  at a predetermined cycle ( 540 ). It should be noted that the name tag type node B  100  also starts the microcomputer  116  when information is input from the user.  
         [0152]     Next, the name tag type node B  100  obtains (senses) various pieces of information by using the sensor  117  ( 541 ).  
         [0153]     Next, the name tag type node B  100  makes an inquiry by radio to the base station  300  about whether the base station  300  holds a message addressed to the name tag type node B  100  ( 542 ).  
         [0154]     Upon reception of the inquiry from the name tag type node B  100 , the base station  300  judges whether it holds a message addressed to the name tag type node B  100  or not.  
         [0155]     If it is judged that the message addressed to the name tag type node B  100  is not held, the base station  300  informs the name tag type node B  100  to that effect.  
         [0156]     On the other hand, if it is judged that the message addressed to the name tag type node B  100  is held, the base station  300  transmits the message to the name tag type node B  100 .  
         [0157]     The name tag type node B  100  receives the inquiry message from the base station  300  ( 543 ).  
         [0158]     Upon reception of the inquiry message, the name tag type node B  100  lights the LED  103  for a fixed time, and sounds the buzzer  111  for a fixed time simultaneously. Accordingly, the name tag type node B  100  notifies the reception of the message to the user.  
         [0159]     Next, the name tag type node B  100  displays the received inquiry message on the LCD  107  ( 544 ).  
         [0160]     The user inputs a reply for the displayed inquiry message to the name tag type node B  100 . The user may also select a reply message to be returned to the name tag type node A  100  from among the reply messages preregistered in the name tag type node B  100 .  
         [0161]     The name tag type node B  100  generates a reply message based on the information input from the user. Then, the generated reply message is transmitted to the base station  300  ( 545 ).  
         [0162]     Next, the name tag type node B  100  turns OFF the displaying on the LCD  107  ( 546 ). The name tag type node B  100  sets the microcomputer  116  in a sleep state ( 547 ).  
         [0163]     Meanwhile, the base station  300  receives the reply message from the name tag type node B  100 , and transfers the received reply message to the server  200 .  
         [0164]     The server  200  receives the reply message from the base station  300 , and determines a destination address of the received reply message. In this case, it is determined that the destination address of the inquiry message is the name tag type node A  100 . A base station  300  that communicates with the determined name tag type node A  100  is retrieved ( 548 ).  
         [0165]     Subsequently, the reply message is transferred to the retrieved base station  300  ( 549 ).  
         [0166]     Then, the base station  300  receives the reply message from the server  200 . The base station  300  holds the received reply message.  
         [0167]     Meanwhile, the name tag type node A  100  starts the microcomputer  116  at a predetermined cycle ( 550 ). It should be noted that the name tag type node A  100  also starts the microcomputer  116  when information is input from the user.  
         [0168]     Next, the name tag type node A  100  obtains (senses) various pieces of information by using the sensor  117  ( 551 ).  
         [0169]     Next, the name tag type node A  100  makes an inquiry by radio to the base station  300  about whether the base station  300  holds a message addressed to the name tag type node A  100  ( 552 ).  
         [0170]     Upon reception of the inquiry from the name tag type node A  100 , the base station  300  judges whether it holds a message addressed to the name tag type node A  100  or not.  
         [0171]     If it is judged that the message addressed to the name tag type node A  100  is not held, the base station  300  informs the name tag type node A  100  to that effect.  
         [0172]     On the other hand, if it is judged that the message addressed to the name tag type node A  100  is held, the base station  300  transmits the message to the name tag type node A  100 .  
         [0173]     The name tag type node A  100  receives the reply message from the base station  300  ( 553 ).  
         [0174]     Upon reception of the reply message, the name tag type node A  100  lights the LED  103  for a fixed time, and sounds the buzzer  111  for a fixed time simultaneously ( 554 ). Accordingly, the name tag type node A  100  notifies the reception of the message to the user.  
         [0175]     Next, the name tag type node A  100  displays the received inquiry message on the LCD  107  ( 555 ).  
         [0176]     The name tag type node A  100  turns OFF the displaying on the LCD  107  after a passage of predetermined time ( 556 ). It should be noted that the name tag type node A  100  also turns OFF the displaying on the LCD  107  when the user executes a message checking operation.  
         [0177]     The name tag type node A  100  sets the microcomputer  116  in a sleep state ( 547 ).  
         [0178]     As described above, the message can be transmitted/received between the name tag type nodes  100 .  
       Second Embodiment  
       [0179]     According to a second embodiment of this invention, entrance/exit control is carried out by using a name tag type node  100 .  
         [0180]      FIG. 14  is a block diagram of a sensor network system according to a second embodiment of this invention.  
         [0181]     The sensor network system includes a name tag type node  100 , a server  200 , a base station  300 , a receiver  400 , and a network  600 .  
         [0182]     The receiver  400  is connected to the server  200  through the network  600 . The receiver  400  monitors surrounding radio waves. Upon detection of an radio wave transmitted from the name tag type node  100 , the receiver  400  notifies a node ID of the corresponding name tag type node  100  to the server  200 . Accordingly, the server  200  can recognize that the name tag type node  100  exists near the receiver  400 .  
         [0183]     The receiver  400  has an radio wave detection sensitivity set lower than that of the base station  300 . Thus, the receiver  400  detects an radio wave alone of a name tag type node  100  in its vicinity.  
         [0184]     The name tag type node  100 , the server  200 , the base station  300 , and the network  600  are similar to those of the sensor network system of the first embodiment shown in  FIG. 1 , and thus description thereof will be omitted.  
         [0185]      FIG. 15  is an explanatory diagram of how the sensor network system of the second embodiment of this invention is installed.  
         [0186]     An area where the sensor network system is installed includes a hallway  915 , a room A  914 , and a room B  913 . A door A  912  and a receiver A  400  are installed on the hallway  915  side of the room A  914 . A door B  911  and a receiver B  400  are installed on the hallway  915  side of the room B  913 . The base station  300  is installed in the hallway  915 .  
         [0187]     Description will be made of a case where a user having a name tag type node  100  moves around the area described above. The name tag type node  100  and the base station  300  carry out normal communication similar to that of the first embodiment.  
         [0188]     In this case, the receiver B• 400  near the name tag type node  100  detects an radio wave issued by the name tag type node  100 . Next, the receiver B  400  determines the name tag type node  100  that has issued the radio wave based on the detected radio wave, and notifies a node ID of the determined name tag type node  100  to the server  200 .  
         [0189]     The receiver B  400  may also measure intensity of the detected radio wave to notify the measured intensity to the server  200 . Hence, the server  200  can detect a position of the name tag type node  100  with high accuracy.  
         [0190]     The server  200  judges whether to allow the user of the name tag type node  100  in the room based on entrance control information. When it is judged that entrance/exit permission is given to the user, the server  200  notifies the receiver B  400  to that effect.  
         [0191]     Upon reception of the entrance/exit permission notification from the server  200 , the receiver B  400  unlocks the door  911 . Further, the receiver B  400  may also control the door  911  to automatically open.  
         [0192]     As described above, the sensor network system of the embodiment according to this invention enables entrance/exit control of the user.  
         [0193]     The name tag type node  100  of the embodiment according to this invention intermittently operates. Thus, when the name tag type node  100  is in a sleep state, the receiver  400  cannot detect the radio wave of the name tag type node  100 .  
         [0194]     Accordingly, when the name tag type node  100  starts communication with the base station  300 , an operation interval thereof is made shorter. When an operation switch  108  is operated, the name tag type node  100  may transmit sensor data to the base station  300 .  
         [0195]      FIG. 16  is a sequential diagram of a position detection process of the sensor network system according to the second embodiment of this invention.  
         [0196]     As shown in  FIG. 16 , the user of the name tag type node  100  moves from a position near the receiver A  400  to a position near the receiver B  400 .  
         [0197]     First, the user of the name tag type node  100  moves close to the receiver A  400 .  
         [0198]     At this time, the name tag type node  100  starts the microcomputer  116  at a predetermined cycle ( 561 ). It should be noted that the name tag type node  100  also starts the microcomputer  116  when information is input from the user.  
         [0199]     Next, the name tag type node  100  turns ON the displaying on the LCD  107  ( 562 ). Next, the name tag type node  100  obtains (senses) various pieces of information by using the sensor  117  ( 563 ).  
         [0200]     Next, the name tag type node  100  transmits the obtained information (sensor data) to the base station  300  ( 564 ).  
         [0201]     Next, the name tag type node  100  turns OFF the displaying on the LCD  107  ( 565 ). The name tag type node  100  then sets the microcomputer  116  in a sleep state ( 566 ).  
         [0202]     Meanwhile, the base station  300  receives the sensor data from the name tag type node  100 , and transfers the received sensor data to the server  200 .  
         [0203]     The server  200  receives the sensor data from the base station  300  ( 567 ).  
         [0204]     At this time, the receiver A  400  near the name tag type node  100  detects an radio wave of the sensor data transmitted from the name tag type node  100  ( 568 ).  
         [0205]     The receiver A  400  determines the name tag type node  100  which has transmitted the radio wave based on the detected radio wave. Then, the receiver A  400  transmits a node ID of the determined name tag type node  100  and its own receiver ID to the server  200  ( 569 ).  
         [0206]     The server  200  then receives the node ID and the receiver ID from the receiver A  400 , and determines a position of the name tag type node  100  based on the received node ID and receiver ID ( 570 ). Specifically, the server  200  determines that the name tag type node  100  exists near the receiver A  400  corresponding to the received receiver ID.  
         [0207]     Next, the user of the name tag type node  100  moves close to the receiver B  400 .  
         [0208]     At this time, the name tag type node  100  starts the microcomputer  116  at a predetermined cycle ( 571 ). It should be noted that the name tag type node  100  also starts the microcomputer  116  when information is input from the user.  
         [0209]     Next, the name tag type node  100  turns ON the displaying on the LCD  107  ( 572 ). The name tag type node  100  obtains (senses) various pieces of information by using the sensor  117  ( 573 ).  
         [0210]     Next, the name tag type node  100  transmits the obtained information (sensor data) to the base station  300  ( 574 ).  
         [0211]     Next, the name tag type node  100  turns OFF the displaying on the LCD  107  ( 575 ). The name tag type node  100  then sets the microcomputer  116  in a sleep state ( 576 ).  
         [0212]     Meanwhile, the base station  300  receives the sensor data from the name tag type node  100 , and transfers the received sensor data to the server  200 .  
         [0213]     The server  200  receives the sensor data from the base station  300  ( 577 ).  
         [0214]     At this time, the receiver B  400  near the name tag type node  100  detects an radio wave of the sensor data transmitted from the name tag type node  100  ( 578 ).  
         [0215]     The receiver B  400  determines the name tag type node  100  which has transmitted the radio wave based on the detected radio wave. Then, the receiver B  400  transmits a node ID of the determined name tag type node  100  and its own receiver ID to the server  200  ( 579 ).  
         [0216]     The server  200  receives the node ID and the receiver ID from the receiver B  400 , and determines a position of the name tag type node  100  based on the received node ID and receiver ID ( 580 ). Specifically, the server  200  determines that the name tag type node  100  exists near the receiver B  400  corresponding to the received receiver ID.  
         [0217]     As apparent from the foregoing, by including the receiver, the sensor network system of the embodiment enables determination of the position of the name tag type node. Hence, the sensor network system of the embodiment can be applied not only to entrance/exit control but also to moving object monitoring.  
         [0218]     This invention can be applied to a name tag carried to be used in an exhibition hall, a lecture hall, a company, a hospital, public facilities, or the like.  
         [0219]     While the present invention has been described in detail and pictorially in the accompanying drawings, the present invention is not limited to such detail but covers various obvious modifications and equivalent arrangements, which fall within the purview of the appended claims.