Communication System

Abstract

Provided are a communication system that makes the structure of a slave more simple, and an information terminal that makes the structure more simple. The communication system includes: a master unit that can send a signal to a slave unit; and a slave unit that has an antenna, a sensor unit, an RFID unit, and a switch that connects the antenna to either the sensor unit or the RFID unit, and if the slave unit receives a switching signal from the master unit via the antenna of the slave unit, the switch of the slave unit switches from a state where the antenna and the sensor unit are connected to a state where the antenna and the RFID unit are connected.

Description

Technical Field

[0001] The present invention relates to a communication system and an information terminal. Background Art

[0002] There has always been a passive wireless transponder (Passive wireless transponder) (for example, refer to patent document 1), which has: an antenna, a rectifier and a modulator for providing a wireless frequency identification (RFID) function by communicating according to the backscattering principle, an oscillator for providing a modulation frequency to the modulator, and a sensing element connected to the oscillator and the oscillation frequency of the oscillator depends on the value of a specified variable sensed by the sensing element, wherein the oscillation frequency is N times the higher harmonic of the modulation frequency.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: JP 2018-517981 Summary of the invention

[0006] Problems to be solved by the invention

[0007] However, existing passive wireless repeaters operate and are controlled by utilizing a radio frequency carrier signal transmitted from a reader, thereby transmitting sensor data to the reader at a plurality of reverse scanning modulation frequencies that can be selected.

[0008] If the passive wireless repeater as a slave with a sensor is equipped with the above-mentioned functions, the structure of the slave becomes complicated. In a system including a reader as a master and passive wireless repeaters as slaves, it is preferred that the structure of the slave is simpler, especially when there are many slaves.

[0009] Therefore, an object is to provide a communication system with a simpler structure of a slave unit and an information terminal with a simpler structure.

[0010] Means for solving problems

[0011] A communication system of an embodiment of the present invention includes: a main machine capable of sending signals to a sub-machine; and a sub-machine, comprising an antenna, a sensor unit, an RFID unit, and a switching switch connecting the antenna to either the sensor unit or the RFID unit, wherein if a switching signal is received from the main machine via the antenna of the sub-machine, the switching switch of the sub-machine switches from a state in which the antenna and the sensor unit are connected to a state in which the antenna and the RFID unit are connected.

[0012] Effects of the Invention

[0013] A communication system with a simpler structure of a slave unit and an information terminal with a simpler structure can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a diagram showing an application example of the communication system 300 according to the embodiment.

[0015] Figure 2 A diagram showing the structure of the communication system 300.

[0016] Figure 3 2 is a diagram showing the configuration of the BS circuit 212 and the sensor 220 .

[0017] Figure 4 The diagram shows the waveforms of a carrier wave, a sensor signal, and a signal obtained by superimposing the sensor signal on the carrier wave.

[0018] Figure 5 2 is a diagram showing an example of an output signal of the BS circuit 212 received by the control device 100 .

[0019] Figure 6 A diagram showing a flowchart showing a process executed by the control device 100 . DETAILED DESCRIPTION

[0020] Hereinafter, embodiments of a communication system and an information terminal to which the present invention is applied will be described.

[0021] <Implementation Method>

[0022] Figure 1 3 is a diagram showing an application example of a communication system 300 according to an embodiment. The communication system 300 includes a control device 100 as a master machine mounted on an unmanned aircraft 50 and a bolt 200 as a slave machine. The bolt 200 is an example of an information terminal and is used to fix a lighting component 20 to an inner wall 11 of a tunnel 10 as an example.

[0023] The bolt 200 includes a sensor for detecting the fixing state to the inner wall 11 and an RFID (Radio Frequency Identifier) ​​chip, and outputs a signal including a detection value of the sensor and a response signal including the ID of the RFID chip. The signal including the output detection value and the response signal are received by the control device 100 mounted on the unmanned aircraft 50.

[0024] When the communication system 300 is applied to the channel 10 as described above, the user of the communication system 300 controls the unmanned aircraft 50 by operating the controller, so that the unmanned aircraft 50 approaches the lighting component 20, and the control device 100 obtains the signal including the detection value and the response signal output from the bolt 200.

[0025] By reading the level of the signal including the detection value, it is possible to check whether looseness occurs in each bolt 200. Many lighting components 20 are installed on the inner wall 11 of the channel 10. Since many bolts 200 are installed for one lighting component 20, many bolts 200 are used for one channel 10.

[0026] In addition, the unmanned aircraft 50 includes a control unit that wirelessly communicates with the controller and controls the rotation speed of multiple motors according to the command sent from the controller. Thus, the unmanned aircraft 50 can fly freely according to the operation of the controller. In addition, the control unit of the unmanned aircraft 50 is connected by a cable or the like so that data communication can be performed with the control device 100 mounted on the unmanned aircraft 50.

[0027] Figure 2 FIG. 3 is a diagram showing the structure of the communication system 300. Figure 2 The control device 100 and the bolt 200 are shown in FIG.

[0028] The control device 100 includes a main control unit 111, a detection value acquisition unit 112, an ID acquisition unit 113, a memory 114, and an antenna 120. The control device 100 is implemented by a computer including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a HDD (Hard Disk Drive), an input / output interface, and an internal bus.

[0029] The main control unit 111, the detection value acquisition unit 112, and the ID acquisition unit 113 are components that represent the functions of the program executed by the control device 100 as functional blocks. In addition, the memory 114 is a component that functionally represents the memory of the control device 100.

[0030] The main control unit 111 is a processing unit that integrates the processing of the control device 100 , and executes processing other than the processing executed by the detection value acquisition unit 112 and the ID acquisition unit 113 .

[0031] The detection value acquisition unit 112 performs control such as transmission of a request signal and adjustment of transmission power in order to acquire the detection value detected by the bolt 200 .

[0032] The ID acquisition unit 113 performs control such as transmission of a switching signal and adjustment of transmission power of the switching signal in order to acquire the ID from the bolt 200 .

[0033] The memory 114 stores the detection value acquired by the detection value acquisition unit 112 , the ID acquired by the ID acquisition unit 113 , and the like.

[0034] The antenna 120 is used for communication with the bolt 200 .

[0035] The bolt 200 includes a circuit chip 210 , a sensor 220 , an RFID chip 230 , and an antenna 240 .

[0036] The circuit chip 210 includes a switch 211, a BS (backscattering) circuit 212, a rectifier circuit 213, and a constant voltage circuit 214. The circuit chip 210 is a chip-type circuit having the switch 211, the BS circuit 212, the rectifier circuit 213, and the constant voltage circuit 214 built therein, but may not be a chip-type circuit.

[0037] The switch 211 is a three-terminal switch having terminals 211A, 211B, and 211C. The switch 211 has an input terminal 211D to which a switching signal transmitted from the control device 100 is input. The terminals 211A, 211B, and 211C are connected to the antenna 240, the BS circuit 212, and the RFID chip 230, respectively.

[0038] Switch 211 connects antenna 240 to either BS circuit 212 or RFID chip 230 according to a switching signal. Switch 211 connects terminal 211A and terminal 211B, that is, antenna 240 and BS circuit 212 when the switching signal is at an L (low) level.

[0039] When the switching signal of the switch 211 is switched to the H (high) level, the switch 211 connects the terminal 211A and the terminal 211C, that is, connects the antenna 240 and the RFID chip 230 .

[0040] The switching signal is maintained at an L level except in a certain state. Therefore, the switching switch 211 connects the antenna 240 and the BS circuit 212 except in a certain state. The switching signal being at an H level has the same meaning as the case where the circuit chip 210 receives a switching signal for switching the connection destination of the antenna 240 from the BS circuit 212 to the RFID chip 230 by the switching switch 211.

[0041] The BS circuit 212 is connected to the switch 211, the rectifier circuit 213, and the sensor 220. When the antenna 240 receives a request signal and the request signal is input via the switch 211, the BS circuit 212 outputs the request signal to the rectifier circuit 213. As a result, the sensor 220 operates and outputs a sensor signal indicating a detection value to the BS circuit 212.

[0042] When a sensor signal is input from the sensor 220, the BS circuit 212 outputs a signal including a detection value indicated by the sensor signal to the switch 211. The signal including the detection value is radiated from the antenna 240, and is received by the control device 100 when the control device 100 is within a receivable range. The details of the BS circuit 212 will be described later.

[0043] The rectifier circuit 213 is a full-wave rectifier circuit provided between the BS circuit 212 and the constant voltage circuit 214, and performs full-wave rectification on the request signal input from the BS circuit 212 and outputs it to the constant voltage circuit 214. The request signal is an AC signal of a predetermined frequency, and is therefore full-wave rectified by the rectifier circuit 213 and output to the constant voltage circuit 214.

[0044] The constant voltage circuit 214 is a smoothing circuit that smoothes the power after full-wave rectification by the rectification circuit 213. The DC power smoothed by the constant voltage circuit 214 is provided as power to act on the BS circuit 212 and the sensor 220. As the constant voltage circuit 214, for example, a smoothing capacitor can be used. The constant voltage circuit 214 functions as a smoothing capacitor and also functions as a power source that provides the stored power to the sensor 220 and the BS circuit 212.

[0045] The sensor 220 has a power input terminal connected to the constant voltage circuit 214, and an output terminal connected to the BS circuit 212. When power is input from the constant voltage circuit 214, the sensor 220 is activated and a detection signal indicating a detection value is output to the BS circuit 212. The sensor 220 is, for example, a pressure sensor sealed inside the bolt 200. As the pressure sensor, for example, a semiconductor pressure sensor using a piezoresistive effect can be used.

[0046] When the member for mounting the lighting member 20 to the inner wall 11 is sandwiched between the bolt 200 and the nut and tightened, the bolt 200 is pulled up in the axial direction to increase the volume of the internal space sealed in the sensor 220 , thereby reducing the pressure.

[0047] Furthermore, if the bolt 200 and the nut are relatively loosened while being fastened with the components for fixing the lighting component 20 to the inner wall 11, the force pulling the bolt 200 in the axial direction is reduced, and the amount of pulling is reduced. As a result, the volume of the internal space enclosed in the sensor 220 is reduced, and the internal pressure is increased. If such a reduction in pressure is detected, the loosening of the bolt 200 and the nut over time can be detected.

[0048] The RFID chip 230 is an IC (Integrated Circuit) chip for an RFID tag, and stores a unique ID in an internal memory. The RFID chip 230 is a passive type without a built-in power supply.

[0049] When the switch 211 connects the antenna 240 and the RFID chip 230, the RFID chip 230 is activated by the power of the signal received by the antenna 240 and outputs a response signal including the ID. The response signal is radiated by the antenna 240 and is received by the control device 100 when the control device 100 is located at a position where the response signal can be received.

[0050] The signal indicating that the RFID chip 230 is powered on is a switching signal of an H level that switches the connection destination of the antenna 240 from the BS circuit 212 to the RFID chip 230 by the switching switch 211 .

[0051] Figure 3 A diagram showing the structure of the BS circuit 212 and the sensor 220.

[0052] The BS circuit 212 includes a switch 251 , a filter 252 , a mixer 253 , a PLL (Phase Locked Loop) 254 , an amplifier 255 , and a control unit 256 .

[0053] The switch 251 is a two-terminal switch, and is switched on / off by the output of the filter 252. For example, a FET (Field Effect Transistor) can be used as the switch 251. One terminal 251A of the switch 251 is connected to the terminal 211B of the changeover switch 211, and the other terminal 251B is grounded.

[0054] The filter 252 is an LPF (Low Pass Filter) provided between the control terminal of the switch 251 and the mixer 253. A signal of a predetermined frequency is input to the filter 252 from the mixer 253. The predetermined frequency is, for example, 920 MHz. The filter 252 cuts off a frequency component higher than a frequency band including the predetermined frequency. The filter 252 is provided to cut off higher harmonics of the signal of the predetermined frequency.

[0055] The mixer 253 superimposes the sensor signal input from the output terminal of the amplifier 255 and amplified on the carrier input from the output terminal of the PLL 254 and outputs the superimposed signal.

[0056] The PLL 254 outputs a carrier wave of a predetermined frequency for transmitting the amplified sensor signal. The frequency of the carrier wave is, for example, 920 MHz.

[0057] The amplifier 255 amplifies the sensor signal input from the sensor 220 and inputs the amplified sensor signal to the mixer 253 .

[0058] The control unit 256 switches the switch 211 (see Figure 2 The control unit 256 is, for example, a microcomputer, and its output terminal is connected to the input terminal 211D of the switch 211.

[0059] If the switching signal of the H level is input to the BS circuit 212 via the switching switch 211, the control unit 256 is activated to switch the connection destination of the antenna 240 based on the switching switch 211 to the RFID chip 230. The period during which the switching signal is at the H level is a prescribed period sufficient for the RFID chip 230 to perform an operation to output a response signal including an ID, and after the prescribed period has passed, the switching signal is changed to the L level. If the switching signal returns to the L level, the control unit 256 switches the connection destination of the antenna 240 based on the switching switch 211 from the RFID chip 230 to the BS circuit 212.

[0060] As an example, the sensor 220 has a structure of a resonant circuit, which has three inverters 221, a variable resistor 222, and a capacitor 223. The three inverters 221 are connected in series. Here, the three inverters 221 are sequentially referred to as the first stage, the middle stage, and the final stage from the right. The output terminal of the first-stage inverter 221 is connected to the input terminal of the inverter 221 of the middle stage, and is connected to its own input terminal via the capacitor 223.

[0061] In addition, the output terminal of the intermediate-stage inverter 221 is connected to the input terminal of the final-stage inverter 221. In addition, the output terminal of the intermediate-stage inverter 221 is connected to its own input terminal via the variable resistor 222 and the capacitor 223, and is connected to the input terminal of the first-stage inverter 221 via the variable resistor 222.

[0062] As described above, the variable resistor 222 is a semiconductor pressure sensor using the piezoresistive effect, and its resistance value changes in accordance with changes in the pressure in the internal space of the bolt 200. The capacitance of the capacitor 223 is a fixed value.

[0063] Since the variable resistor 222 changes according to the change in pressure in the internal space of the bolt 200, when the power of the request signal is provided and activated, this sensor 220 outputs a sensor signal of a resonant frequency corresponding to a time constant determined by the resistance value of the variable resistor 222 and the electrostatic capacitance of the capacitor 223.

[0064] The sensor signal is amplified by the amplifier 255, superimposed on the carrier input from the PLL 254 in the mixer 253, and the high harmonic components are removed by the filter 252 and input to the control terminal of the switch 251. As a result, the switch 251 is switched on / off at the frequency of the signal output from the filter 252. The output of the switch 251 is a signal including a detection value, which is radiated from the antenna 240 via the switching switch 211 as an output signal of the BS circuit 212.

[0065] Figure 4 The figure shows the waveform of the carrier, the sensor signal, and the signal with the sensor signal superimposed on the carrier. As an example, when the carrier is 920 MHz, the time constant of the resonant circuit of the sensor 220 is set so that the frequency of the sensor signal is about 100 kHz to 1 MHz (about 1 / 1000 to 1 / 10000 of the carrier).

[0066] As an example, if the sensor signal of 100 kHz shown in (B) is superimposed on the carrier of 920 MHz shown in (A), the superimposed signal shown in (C) is obtained. The superimposed signal is a signal obtained by modulating the phase of the carrier with the sensor signal. The superimposed signal is input from the filter 252 to the control terminal of the switch 251.

[0067] Figure 5 2 is a diagram showing an example of an output signal of the BS circuit 212 received by the control device 100 . Figure 5 An example of a waveform when the control device 100 receives output signals of the BS circuit 212 from the two bolts 200 is shown.

[0068] Since the resistance value of the variable resistor 222 of the sensor 220 changes according to the pressure of the internal space of the bolt 200 , the resonance frequency of the sensor signal changes according to the pressure of the internal space of the bolt 200 .

[0069] exist Figure 5 The output signal of the BS circuit 212 received from one bolt 200 has a peak at about 100 kHz before and after the 920 MHz carrier, and the output signal of the BS circuit 212 received from the other bolt 200 has a peak at about 200 kHz before and after the 920 MHz carrier.

[0070] Figure 6 A diagram showing a flowchart representing a process executed by the control device 100 .

[0071] The user operates the unmanned aircraft 50 using the controller, and when the unmanned aircraft 50 is close to the inner wall 11 of the passage 10 to a certain extent, the control device 100 starts processing (activation).

[0072] The detection value acquisition unit 112 transmits a request signal at a predetermined transmission power (step S1). The request signal is transmitted to an unspecified bolt 200. As a result, the bolt 200 that has received the request signal outputs a signal including a detection value.

[0073] The detection value acquisition unit 112 determines whether a signal including a detection value is received from the bolt 200 (step S2 ).

[0074] When the detection value acquisition unit 112 determines that a signal including a detection value has been received ( S2 : Yes), it reduces the transmission power of the request signal by a predetermined power (step S3 ).

[0075] On the other hand, if the detection value acquisition unit 112 determines in step S2 that a signal including a detection value has not been received ( S2 : No), it increases the transmission power of the request signal to the predetermined power before being reduced in the process of the immediately preceding step S3 (step S4 ).

[0076] The detection value acquisition unit 112 determines whether a signal including a detection value is received from the bolt 200 (step S5). This is to confirm whether the transmission power determined to be last received in step S2 can be received again.

[0077] If the detection value acquisition unit 112 determines that the signal including the detection value is not received (S5: No), the main control unit 111 advances the flow to step S6, and requests the control unit of the unmanned aircraft 50 to make the unmanned aircraft 50 closer to the bolt 200 (step S6). As a result, the control unit of the unmanned aircraft 50 displays a request to the controller to make the unmanned aircraft 50 closer to the bolt 200.

[0078] If the detection value acquisition unit 112 determines in step S5 that a signal including a detection value is received (S5: Yes), it determines whether there is one signal including a detection value (step S7). Figure 5 As shown, two peaks are obtained on both sides of the peak of the carrier wave, which are deviated from the peak of the carrier wave by the resonance frequency of the sensor 220. Therefore, in step S7, it is only necessary to determine whether there is one peak on each side of the peak of the carrier wave.

[0079] If the detected value acquisition unit 112 determines that there is not one signal including the detected value (S7: No), the transmission power of the request signal is reduced by a predetermined power (step S8). This is because there is only one signal including the detected value.

[0080] In step S7 , if the detected value acquisition unit 112 determines that there is one signal including the detected value ( S7 : Yes), the ID acquisition unit 113 transmits a switching signal while maintaining the transmission power set for the request signal in step S4 (step S9 ).

[0081] The ID acquisition unit 113 determines whether a response signal including an ID is received from the bolt 200 (step S10 ).

[0082] When the ID acquisition unit 113 determines that a response signal including an ID is received from the bolt 200 ( S10 : Yes), it determines whether there is one response signal including an ID (step S11 ).

[0083] If the ID acquisition unit 113 determines that there is one response signal including an ID (S11: Yes), the main control unit 111 associates the ID included in the received response signal with the detection value included in the signal determined to be one in step S7 and stores them in the memory 114 (step S12).

[0084] The control device 100 ends a series of processing as described above (END).

[0085] If the ID acquisition unit 113 determines in step S10 that a response signal including an ID has not been received from the bolt 200 ( S10 : No), the main control unit 111 returns the flow to step S6 . This is because the unmanned aircraft 50 is required to be brought closer to the bolt 200 .

[0086] If the ID acquisition unit 113 determines in step S11 that there is not one response signal including an ID (S11: No), the transmission power of the switching signal is reduced by a predetermined power (step S13). This is because a response signal including an ID is received from one bolt 200.

[0087] As described above, when the bolt 200 receives the request signal from the control device 100 , the circuit chip 210 operates with the power of the request signal and obtains a sensor signal indicating the detection value of the sensor 220 , and the BS circuit 212 outputs a signal including the detection value and radiates it from the antenna 240 .

[0088] The control device 100 reduces the transmission power until one of the bolts 200 transmits a signal including a detection value in response to the request signal. Figure 5As shown in FIG. 1 , the signal including the detection value presents a peak value that deviates from the resonance frequency of the sensor 220 on both sides of the peak value of the carrier. On both sides of the peak value of the carrier are peak values ​​that deviate from the resonance frequency of the sensor 220. The control device 100 obtains the signal including the detection value from one bolt 200, and extracts the detection value of the sensor 220 based on the signal including the detection value.

[0089] Furthermore, the control device 100 sends a switching signal while concentrating the communication objects on one bolt 200. If the bolt 200 receives the switching signal, the switching switch 211 switches to a state of connecting the antenna 240 and the RFID chip 230, and the RFID chip 230 operates with the power of the switching signal and outputs a response signal including the ID, and the response signal including the ID is radiated from the antenna 240.

[0090] When the control device 100 obtains a response signal including an ID from the bolt 200 that received the signal including the detection value, the detection value is associated with the ID and stored in the memory 114. Thus, the control device 100 can obtain the detection value detected by the sensor 220 of a certain bolt 200 in association with the ID.

[0091] In such a series of processing, the bolt 200 operates only according to the request signal and the switching signal sent from the control device 100, and the control device 100 performs control for concentrating the bolts 200 of communication into one, and for obtaining a response signal including an ID from the concentrated bolt 200.

[0092] Therefore, it is possible to provide the communication system 300 in which the structure of the bolt 200 (slave unit) is further simplified, and the bolt 200 in which the structure is further simplified.

[0093] In addition, the bolt 200 operates with the power of the request signal and emits a signal including the detection value, and operates with the power of the switching signal and emits a response signal including the ID, so a power source including a battery is not required. In this regard, the structure of the bolt 200 (slave) can also be simplified.

[0094] Furthermore, since the circuit chip 210 of the bolt 200 includes the BS circuit 212, the detection value of the sensor 220 can be processed in analog form without being subjected to processing such as digital conversion and the detection value can be transmitted to the control device 100. In this regard, the structure of the bolt 200 (slave) can also be simplified.

[0095] In addition, the above description describes a method in which the sensor 220 is provided on the bolt 200 (sub-machine) and the detection value and ID are obtained by the control device 100 (main machine) mounted on the unmanned aircraft 50, but the sub-machine provided with the sensor 220 and the RFID chip 230 is not limited to the bolt 200, and the control device 100 as the main machine is not limited to the method of being mounted on the unmanned aircraft 50. The sensor 220 and the RFID chip 230 can be provided on various sub-machines, and the detection value and ID can be obtained by the control device 100 of various methods.

[0096] In addition, the above description is made of the circuit chip 210 and the RFID chip 230 being separate bodies in the bolt 200. In this way, by making the circuit chip 210 and the RFID chip 230 separate bodies, the procurement cost can sometimes be reduced. In addition, the circuit chip 210 and the RFID chip 230 are also configured as one chip.

[0097] As mentioned above, the communication system and the information terminal according to the exemplary embodiments of the present invention have been described, but the present invention is not limited to the specifically disclosed embodiments, and various modifications and changes can be made without departing from the scope of the claims.

[0098] In addition, the present international application claims priority based on Japanese Patent Application No. 2019-143048 filed on August 2, 2019, the entire contents of which are incorporated herein by reference.

[0099] Explanation of symbols

[0100] 50 drones

[0101] 100 control devices

[0102] 111 Main control unit

[0103] 112 Detection value acquisition unit

[0104] 113ID Acquisition Department

[0105] 114 Memory

[0106] 200 bolts

[0107] 210 circuit chip

[0108] 211 Switch

[0109] 212BS circuit

[0110] 220 Sensors

[0111] 230RFID chip

[0112] 240 Antenna

[0113] 300 communication system.

Claims

1. A communication system, comprising: The master unit can send signals to the slave units; and The slave unit includes an antenna, a sensor unit, an RFID unit, a switch for connecting the antenna to either the sensor unit or the RFID unit, and a switching circuit for switching the switch based on a switching signal transmitted from the master unit. If a switching signal is received from the main unit via the antenna of the slave unit, the switching circuit switches the switching switch of the slave unit from a state in which the antenna and the sensor unit are connected to a state in which the antenna and the RFID unit are connected according to the switching signal, The slave device further includes a reverse scanning circuit provided between the switching switch and the sensor unit. The switching switch is a switching switch for switching between a state in which the antenna is connected to the sensor unit via the reverse scanning circuit and a state in which the antenna is connected to the RFID unit. When the switching switch of the slave unit is in a state where the antenna is connected to the sensor unit via the reverse scanning circuit, if a request signal is received from the master unit via the antenna of the slave unit, a signal including a detection value output by the sensor unit is transmitted from the antenna to the master unit via the reverse scanning circuit. When receiving the signal including the detection value from the plurality of the slaves, the master reduces the transmission output of the request signal until the master receives the signal including the detection value from one of the slaves.

2. The communication system according to claim 1, wherein: The sensor unit and the reverse scanning circuit operate using power of a request signal received through the antenna.

3. The communication system according to claim 1 or 2, wherein: If the changeover switch is switched to a state in which the antenna and the RFID unit are connected, the RFID unit outputs a signal including identification information via the antenna.

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