JP2018190053A - Sensor module and sensor network using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably acquire data with periodicity.SOLUTION: A sensor module 1 comprises: a power supply circuit 10 including an environment power generation section 11 and a power storage section 12; a sensor circuit 20 to be intermittently operated by receiving power supply from the power supply circuit 10; and a voltage monitoring circuit 30 for normally monitoring an input voltage Vin stored in the power storage section 12. The sensor circuit 20 alternately repeats an active state in which a measurement object is measured and a measurement result is wirelessly transmitted and a sleep state in which the actions are stopped. Output confirmation is performed concerning the voltage monitoring circuit 30 by a predetermined cycle in the sleep state. A state is returned to the active state when the input voltage Vin is higher than a predetermined reference voltage Vref. The sleep state is kept when the input voltage Vin is lower than the reference voltage Vref.SELECTED DRAWING: Figure 2

Description

  The invention disclosed in this specification relates to a sensor module and a sensor network using the same.

  In recent years, sensor modules that operate using self-generated power by energy harvesting (so-called energy harvesting) have been put into practical use. Since such a sensor module can be suitably applied to an application where it is difficult to install power supply wiring or replace a battery, it is expected to be widely used in various applications.

JP 2011-13765 A JP 2016-11909 A

  By the way, in the environmental power generation, since stable generated power is not always obtained, intermittent operation of the sensor module is essential. However, in the conventional sensor module, there is a possibility that data acquisition and transmission may be interrupted due to power shortage, and there is room for further improvement in operation stability. Further, in the conventional sensor module, since the cycle of the intermittent operation depends on the generated power of the environmental power generation device and the power consumption of the sensor module, it is difficult to acquire data having periodicity.

  Patent Document 1 discloses a sensor network terminal that detects the amount of power generated and the amount of electricity stored in an environmental power generation device, transmits the detected amount to a system manager, and changes the setting of a measurement cycle in accordance with an instruction from the system manager. Yes. However, this sensor network terminal does not change the setting of the measurement cycle by itself and requires a system manager separately.

  Patent Document 2 collects data every predetermined period, determines whether desired stored power is ensured by vibration power generation, and performs wireless transmission of data according to the determination result. A vibration power generation wireless sensor for determining whether or not is disclosed. However, since this vibration power generation wireless sensor always collects data even when wireless transmission of data is not performed due to power shortage, there is room for further improvement in power saving. .

  In view of the above-mentioned problems found by the inventors of the present application, the invention disclosed in this specification is a sensor module that can stably acquire periodic data, and a sensor network using the same The purpose is to provide.

  A sensor module disclosed in the present specification is stored in a power supply circuit including an environmental power generation unit and a power storage unit, a sensor circuit that operates intermittently by receiving power supply from the power supply circuit, and the power storage unit A voltage monitoring circuit that constantly monitors an input voltage, and the sensor circuit alternately repeats an active state in which measurement of a measurement target and wireless communication of a measurement result are performed and a sleep state in which the operation is suspended In the sleep state, the output of the voltage monitoring circuit is confirmed at a predetermined cycle. When the input voltage is higher than a predetermined reference voltage, the active state is restored, and the input voltage is higher than the reference voltage. If it is low, the sleep state is maintained (first configuration).

  In the sensor module having the first configuration, the power supply circuit may further include a power management unit (second configuration) that generates a power supply voltage from the input voltage and supplies the power supply voltage to the sensor circuit. .

  In the sensor module having the first or second configuration, the voltage monitoring circuit includes a reset IC that generates a reset signal corresponding to a comparison result between the input voltage and the reference voltage, and the sensor circuit includes: A configuration (third configuration) may be employed in which the logic level of the reset signal is checked to determine whether or not the input voltage is higher than the reference voltage.

  In the sensor module having the first or second configuration, the voltage monitoring circuit includes a resistor ladder that generates a divided voltage of the input voltage, and the sensor circuit calculates a voltage value of the divided voltage. You may make it the structure (4th structure) which confirms and determines whether the said input voltage is higher than the said reference voltage.

  The sensor module having any one of the first to fourth configurations may have a configuration (fifth configuration) in which the energy source of the environmental power generation unit and the measurement target of the sensor circuit are common.

  A sensor network disclosed in the present specification includes a sensor module having any one of the first to fifth configurations, and a receiver that wirelessly receives a measurement result of the sensor module ( Sixth configuration).

  The sensor network having the sixth configuration may be configured to further include a server (seventh configuration) that receives a measurement result of the sensor module from the receiver and records and analyzes the result.

  In the sensor network having the sixth or seventh configuration, the receiver may be configured to be shared by a plurality of sensor modules (eighth configuration).

  In the sensor network having the eighth configuration, each of the plurality of sensor modules may be configured to perform wireless communication while shifting the timing with reference to the time of the built-in clock (9th configuration).

  In the sensor network having the eighth configuration, each of the plurality of sensor modules is configured to perform wireless communication after confirming that other sensor modules are not performing wireless communication (tenth configuration). Good.

  In the sensor network having the eighth configuration, the plurality of sensor modules may be configured to perform wireless communication in designated time slots (eleventh configuration).

  According to the invention disclosed in the present specification, it is possible to provide a sensor module that can stably acquire periodic data and a sensor network using the sensor module.

The figure which shows 1st Embodiment of a sensor network. The figure which shows one structural example of a sensor module Time chart showing comparative example of intermittent operation (without voltage monitoring) Flow chart showing an example of intermittent operation (with voltage monitoring) Time chart showing an example of intermittent operation (with voltage monitoring) Time chart showing periodicity of data acquisition timing The figure which shows 1st Example of a voltage monitoring circuit The figure which shows 2nd Example of a voltage monitoring circuit. The figure which shows 2nd Embodiment of a sensor network. Time chart showing an example of collision avoidance technique The figure which shows an example of a TSA [time slot assign] technique

<Sensor network (first embodiment)>
FIG. 1 is a diagram illustrating a first embodiment of a sensor network. The sensor network X of the present embodiment includes a sensor module 1, a receiver 2, and a server 3.

  The sensor module 1 is a terminal that operates using self-generated power generated by energy harvesting, and measures a predetermined measurement target (= machine vibration or the like). The sensor module 1 has a one-way or two-way wireless communication function, and transmits its measurement result to the receiver 2 wirelessly.

  The receiver 2 is a communication device that wirelessly receives the measurement result of the sensor module 1 and transfers it to the server 3 by wire or wirelessly.

  The server 3 records and analyzes the measurement result of the sensor module 1 transferred from the receiver 2.

  In the sensor network X of the present embodiment, since the power consumption of the sensor module 1 is covered by energy harvesting, the sensor module 1 does not require power supply wiring or battery replacement. In addition, since wireless communication is performed between the sensor module 1 and the receiver 2, no signal wiring is required between them. Therefore, it becomes possible to arrange the sensor module 1 at an arbitrary location.

  For example, when monitoring vibration or temperature of the vehicle using the sensor network X, it is possible to reduce the weight of the vehicle by omitting power supply wiring and signal wiring to the sensor module 1. When monitoring patient biological information using the sensor network X, the sensor module 1 is embedded in the patient's body, and the detection result is read by the receiver 2 outside the body, thereby reducing the burden on the patient. It is possible. In addition, when monitoring vibrations or temperatures of air conditioners, compressors, etc. in factories or the like, it is possible to reduce disconnections caused by transport vehicles and accidents caused by wiring.

<Sensor module>
FIG. 2 is a diagram illustrating a configuration example of the sensor module 1. The sensor module 1 of this configuration example includes a power supply circuit 10, a sensor circuit 20, and a voltage monitoring circuit 30.

  The power supply circuit 10 is a means for supplying power to each part of the sensor module 1, and includes an environmental power generation unit 11, a power storage unit 12, and a power management unit 13.

  The environmental power generation unit 11 is a means (so-called energy harvester) that generates power by receiving energy (= vibration, light, heat, etc.) existing in the environment where the sensor module 1 is placed. When vibration is used as an energy source, a piezoelectric element such as a piezoelectric element may be used as the power generation element. In addition, when sunlight or illumination light is used as an energy source, a silicon-based, compound-based, or organic photoelectric element may be used as the power generation element. When heat is used as an energy source, a thermoelectric element such as a Peltier element may be used as the power generation element. Further, if the energy harvesting (or self-power generation) is understood in a broader sense, a CT current sensor can also be used. The principle is that an alternating current (secondary current) corresponding to the winding ratio flows in the secondary winding so as to cancel the magnetic flux generated in the magnetic core due to the alternating current flowing in the measurement conductor (primary side). Is. However, the above is merely an example, and a power generation device based on another power generation principle may be used. For example, vibration power generation includes not only a piezoelectric type (using a piezo element) but also an electromagnetic induction type (using electromagnetic induction using a coil and a magnet), an electrostatic type (using an electret), and the like.

  The power storage unit 12 is a means for storing the self-generated power obtained by the environmental power generation unit 11 (however, when a CT current sensor is used, it may be read as non-contact power supply power). The generic name of the double layer capacitor) can be preferably used. The input voltage Vin (= charge voltage of the supercapacitor) stored in the power storage unit 12 is supplied to the power management unit 13 and is monitored by the voltage monitoring circuit 30.

  The power management unit 13 generates a desired power supply voltage Vdd from the input voltage Vin and supplies it to the sensor circuit 20. For example, a DC / DC converter can be suitably used as the power management unit 13.

  The sensor circuit 20 includes a sensor unit 21, a wireless communication unit 22, and a control unit 23, and operates intermittently upon receiving power supply from the power supply circuit 10.

  The sensor unit 21 is a predetermined measurement target (magnetism, acceleration, angular velocity, pressure, strain, vibration, temperature, humidity, light, infrared, ultraviolet, electromagnetic wave, radiation, electric field, current, voltage, power, position, distance, displacement, It is a means for measuring flow rate, flow rate, component, composition, concentration, sound, gas, odor, electrical conductivity, pH, water level, count, etc.). The sensor unit 21 may be an analog output or a digital output.

  In the sensor module 1, the energy source of the energy harvesting unit 11 and the measurement target of the sensor unit 21 are preferably common. As one example, the case where the energy generation unit 11 uses vibration as an energy source and the sensor unit 21 uses the above vibration as a measurement target. In this case, when the sensor unit 21 attempts to measure the vibration, the environmental power generation unit 11 receives the vibration and generates electric power. Therefore, the sensor unit 21 is more reliably transferred to the sensor unit 21 as compared with the case where the energy source other than the vibration is used. It is possible to supply power.

  The wireless communication unit 22 wirelessly transmits the measurement result obtained by the sensor unit 21 to the receiver 2.

  The control unit 23 is a control subject of the sensor unit 21 and the wireless communication unit 22, and includes an interface circuit that receives an output signal of the sensor unit 21, a digital control circuit that performs various signal processing, and the like. As the control unit 23, MCU [micro control unit] or the like is preferably used.

  The voltage monitoring circuit 30 constantly monitors the input voltage Vin stored in the power storage unit 12 and sends the monitoring result to the control unit 23 as an output signal So.

  Note that the harvester capability of the energy harvesting unit 11 is not necessarily large, and it is difficult to keep the sensor circuit 20 continuously operating. Therefore, the sensor circuit 20 confirms the output signal So of the voltage monitoring circuit 30 at a predetermined period T, and performs an active state in which measurement of a measurement target and wireless communication of a measurement result are performed, and sleep in which the operation is temporarily suspended. The intermittent operation which repeats a state alternately is performed. Hereinafter, the intermittent operation of the sensor circuit 20 will be described in detail.

<Intermittent operation>
First, prior to the description of the intermittent operation using the voltage monitoring circuit 30, as a comparative example, the intermittent operation without using the voltage monitoring circuit 30 will be briefly described with reference to FIG.

  FIG. 3 is a time chart showing a comparative example of intermittent operation (without voltage monitoring). The input voltage Vin and the operation state of the sensor circuit 20 (A: active state, S: sleep state) are shown in order from the top. Yes. The on-voltage Von is a voltage at which the power management unit 13 is turned on, and the off-voltage Voff is a voltage at which the power management unit 13 is turned off.

  As shown in the figure, the sensor circuit 20 performs an intermittent operation in which the active state A (= measurement and wireless communication) and the sleep state S (= charge) are alternately repeated. In this figure, for the convenience of illustration, the time for maintaining the active state A (for example, times t11 to t12) is depicted longer than the original, but in practice, the time for maintaining the sleep state S (= intermittent operation) Compared to the period T (for example, several minutes to several hours), the process is completed in a very short time.

  If the stored power in the sleep state S is larger than the power consumption in the active state A, after the input voltage Vin once exceeds the on voltage Von, it does not fall below the off voltage Voff. Therefore, the sensor circuit 20 can perform an intermittent operation while maintaining a constant period T.

  On the other hand, as shown in the figure, when the stored power in the sleep state S is smaller than the power consumption in the active state A, the input voltage Vin gradually decreases every time the sleep state S returns to the active state A. Eventually, the voltage drops below the off voltage Voff. As a result, the power management unit 13 is turned off and the power supply to the sensor circuit 20 is stopped, so that the timer of the control unit 23 expires and the intermittent operation cannot be performed at a constant period T (time t12 to t13). And time t14 to t15 for comparison, T ≠ T ′). As described above, if the cycle T of the intermittent operation fluctuates, it becomes impossible to acquire data having periodicity.

  Also, when the input voltage Vin falls below the off voltage Voff during the active state A, measurement and wireless communication are interrupted, so that sufficient data cannot be acquired or all data Cannot be transmitted (see times t13 to t14).

  The above problem can be improved somewhat by adjusting the on-voltage Von and off-voltage Voff of the power management unit 13, but cannot be fundamentally solved. Hereinafter, an intermittent operation that can fundamentally solve the above-described problems by using the voltage monitoring circuit 30 will be described in detail.

  FIG. 4 is a flowchart illustrating an example of the intermittent operation using the voltage monitoring circuit 30. When the power generation operation of the environmental power generation unit 11 is started by the activation of the sensor module 1, the input voltage Vin stored in the power storage unit 12 increases. In step S1, when the input voltage Vin reaches the on voltage Von, the power management unit 13 is turned on in the subsequent step S2.

  As a result, power supply to the sensor circuit 20 is started, so that the sensor circuit 20 is turned on in step S3. Thereafter, in step S4, the measurement target is measured by the sensor unit 21, and further, in step S5, wireless communication of the measurement result by the wireless communication unit 22 is performed. Note that these steps S3 to S5 correspond to the aforementioned active state.

  When the wireless communication in step S5 is completed, the sensor circuit 20 is turned off in the subsequent step S6. That is, the sensor circuit 20 shifts from the active state to the sleep state. However, even after the transition to the sleep state, circuit elements (such as the timer of the control unit 23) necessary for the return to the active state continue to operate with the minimum power supply from the power management unit 13. .

  Thereafter, in step S7, the control unit 23 determines whether or not the period T has elapsed. Here, when a yes determination is made, the flow proceeds to step S8, and when a no determination is made, the flow returns to step S7.

  If a positive determination is made in step S7, in step S8, the control unit 23 checks the output signal So of the voltage monitoring circuit 30, and determines whether or not the input voltage Vin is higher than a predetermined reference voltage Vref. Done. Although not explicitly shown in this flow, it is assumed that the voltage monitoring circuit 30 constantly monitors the input voltage Vin without depending on the operation state of the sensor circuit 20. Here, when a positive determination is made, the flow is returned to step S3, and the return from the sleep state to the active state is performed. On the other hand, when a negative determination is made, the flow is returned to step S7, and the determination of the elapse of the cycle T is repeated.

  That is, in this flow, in the sleep state (steps S6 to S8), the output of the voltage monitoring circuit 30 is confirmed at a predetermined period T. If the input voltage Vin is higher than the predetermined reference voltage Vref, the active state is established. When the input voltage Vin is lower than the reference voltage Vref, the sleep state is maintained. In other words, the loop is rotated so that the sleep state of the period T is repeated until the input voltage Vin exceeds the reference voltage Vref. ing.

  FIG. 5 is a time chart showing an example of an intermittent operation using the voltage monitoring circuit 30. Similarly to FIG. 3, the input voltage Vin and the operation state of the sensor circuit 20 (A: active state, S : Sleep state).

  Note that the above-described reference voltage Vref is at least the input voltage Vin in the active state A (see times t21 to t22, times t23 to t24, or times t26 to t27) with respect to the off voltage Voff of the power management unit 13. Is assumed to be set to a voltage value (Vref ≧ Voff + Δ) that is higher by the assumed drop value Δ.

  After completion of the active state A at time t21 to t22 (corresponding to steps S3 to S5 in FIG. 4), at time t22, the sensor circuit 20 shifts from the active state A to the sleep state S (corresponding to step S6 in FIG. 4). . Therefore, the input voltage Vin starts to increase from the decrease.

  After that, at time t23, with the passage of the cycle T (corresponding to step S7 = Y in FIG. 4), the return determination from the sleep state S to the active state A (corresponding to step S8 in FIG. 4) is performed. In the example of this figure, since the input voltage Vin exceeds the reference voltage Vref at time t23, the return from the sleep state S to the active state A is recognized (corresponding to step S8 = Y in FIG. 4). . Therefore, the input voltage Vin changes from rising to lowering.

  Further, after completion of the active state A at time t23 to t24 (corresponding to steps S3 to S5 in FIG. 4), at time t24, the sensor circuit 20 shifts again from the active state A to the sleep state S (step S6 in FIG. 4). Equivalent). Accordingly, the input voltage Vin starts to rise again from the fall.

  After that, at time t25, with the passage of the cycle T (corresponding to step S7 = Y in FIG. 4), a return determination from the sleep state S to the active state A (corresponding to step S8 in FIG. 4) is performed. However, in the example of this figure, since the input voltage Vin does not exceed the reference voltage Vref at time t25, the return from the sleep state S to the active state A is not recognized, and the sleep state S is maintained (FIG. 4 corresponds to step S8 = N). Therefore, the input voltage Vin continues to rise without turning down.

  After the return to the active state A is postponed at time t25, at time t26, the sleep state S changes to the active state A again with the passage of the second cycle T (corresponding to step S7 = Y in FIG. 4). Is determined (corresponding to step S8 in FIG. 4). In the example of this figure, since the input voltage Vin exceeds the reference voltage Vref at the time t26, the return from the sleep state S to the active state A is not recognized, and the sleep state S changes to the active state A. A return is recognized (corresponding to step S8 = Y in FIG. 4). Therefore, the input voltage Vin changes from rising to lowering.

  Also after time t26, the intermittent operation using the voltage monitoring circuit 30 is continued by repeating the same operation as described above. According to such an operation algorithm, the sensor module 1 can always continue to operate in a safe voltage range (Vin> Voff).

  Therefore, since the operation is not interrupted in the middle of the active state A, it is possible to prevent a problem that sufficient data cannot be acquired or all data cannot be transmitted. It becomes possible to do.

  Further, according to the above operation algorithm, as shown in FIG. 6, the data acquisition interval is n times the period T (where n is a natural number and varies depending on the harvester capability of the energy harvesting unit 11). Value). Therefore, it is possible to acquire data with periodicity, and it becomes possible to predict in advance the timing at which the receiver 2 should read data.

  6 (= time t31, t32, t34, t37) indicates the timing at which data acquisition is performed, and x mark (= time t33, t35, t36) in FIG. 6 indicates data acquisition. Indicates the skipped timing. Accordingly, the data acquisition intervals in this figure are T (= time t31 to t32), 2T (= time t32 to t34), and 3T (= time t34 to t37).

  For example, when the vibration of the motor is to be measured at regular intervals, in the existing sensor network, when the harvester capability of the energy harvesting unit 11 is low, the cycle of the intermittent operation itself varies. It cannot be predicted.

  On the other hand, with the sensor network X of this configuration example, even if the harvester capability of the energy harvesting unit 11 is low, it is always determined whether or not data can be acquired at a constant cycle T (see steps S7 and S8 in FIG. 4). Is done. That is, the data acquisition interval is standardized to a length n times (= n × T) with a predetermined period T as a reference. Therefore, if data is read for every period T, there is no possibility of missing at least data.

  Moreover, if it is the sensor module 1 of this structural example, said intermittent operation | movement can be implement | achieved using its own voltage monitoring circuit 30. FIG. Therefore, unlike the prior art disclosed in Patent Document 1, the intermittent operation cycle T can be determined by itself without requiring a separate system manager, so that the sensor network X can be constructed more easily.

  Further, in the sensor module 1 of this configuration example, the measurement target measurement (step S4 in FIG. 4) and wireless communication of the measurement result (step S5 in FIG. 4) are set, and the sleep state S is changed to the active state A. As long as the input voltage Vin does not exceed the reference voltage Vref at the time of return determination, both operations are skipped.

  By adopting such a configuration, when the harvester capability of the energy harvesting unit 11 is insufficient, not only the measurement result wireless communication but also the measurement target measurement is skipped, and the power storage unit 12 is devoted to charging. be able to. Therefore, it is possible to further reduce power consumption (and thus shorten the data acquisition interval n × T) as compared with the prior art disclosed in Patent Document 2. In Patent Document 2, the amount of power storage is confirmed before data is transmitted, but the power storage is not confirmed before data is acquired or stored. For this reason, there is a possibility that energy may be insufficient during data acquisition or storage, resulting in inoperability. That is, in Patent Document 2, there is no guarantee that sufficient data can be acquired and stored. Therefore, it can be said that the sensor module 1 of this configuration example has an advantage in terms of not only low power consumption but also system stability.

  Further, with the sensor module 1 of this configuration example, the sensor network X can continue to operate stably for a long time even when the harvester capability of the energy harvesting unit 11 is relatively low. Become. Therefore, for example, it can be said to be very suitable as a monitoring means for infrastructure equipment and FA [factory automation] equipment.

<Voltage monitoring circuit (first embodiment)>
FIG. 7 is a diagram illustrating a first embodiment of the voltage monitoring circuit 30. The voltage monitoring circuit 30 of this embodiment includes a reset IC 31 and a pull-up resistor 32.

  The reset IC 31 is a semiconductor integrated circuit device that generates an output signal So (= reset signal) according to a comparison result between the input voltage Vin and the reference voltage Vref and sends the output signal So to the control unit 23. A MOS (metal oxide semiconductor) field effect transistor N1 is integrated.

  The comparator CMP compares the input voltage Vin input to the inverting input terminal (−) and the reference voltage Vref input to the non-inverting input terminal (+) to generate the gate signal Vg. The gate signal Vg becomes low level when the input voltage Vin is higher than the reference voltage Vref, and becomes high level when the input voltage Vin is lower than the reference voltage Vref. Since the comparator CMP has hysteresis, even if the input voltage Vin fluctuates in the vicinity of the reference voltage Vref, the logic level of the gate signal Vg is unlikely to become unstable.

  The transistor N1 is a switch element that forms an open drain type output stage, and is connected between the output terminal of the output signal So and the ground terminal. The transistor N1 is turned on when the gate signal Vg is at a high level, and is turned off when the gate signal Vg is at a low level. Note that an open collector type output stage may be formed by using an npn type bipolar transistor as the transistor N1.

  The pull-up resistor 32 is connected between the input terminal of the power supply voltage Vdd and the output terminal of the output signal So. Therefore, the output signal So is a binary signal that is pulse-driven between the power supply voltage Vdd and the ground voltage GND in accordance with on / off of the transistor N1.

  The control unit 23 checks the logic level of the output signal So to determine whether or not the input voltage Vin is higher than the reference voltage Vref. More specifically, when the output signal So is at a high level (= Vdd), it is determined that the input voltage Vin is higher than the reference voltage Vref, and when the output signal So is at a low level (= GND) It is determined that the signal Vin is lower than the reference voltage Vref.

  As described above, if the reset IC 31 and the pull-up resistor 32 are used, the voltage monitoring circuit 30 with a small area can be realized with a small number of parts. Therefore, even if the voltage monitoring circuit 30 is mounted, the sensor module 1 is unnecessary. It is not necessary to increase the size.

  In particular, if the reset IC 31 having an open drain type output stage is used, the peak value of the output signal So can be obtained simply by externally attaching a pull-up resistor 32 between the input terminal of the power supply voltage Vdd and the output terminal of the output signal So. (= Vdd−GND) can be kept within the input dynamic range of the control unit 23.

  Moreover, many variations of the input dynamic range and the reference voltage are prepared for the commercially available reset IC. Therefore, the voltage monitoring circuit 30 according to the harvester capability of the energy harvesting unit 11 can be realized simply by selecting an appropriate model as the reset IC 31 from commercially available products. It can be said that such specifications are suitable for constantly changing energy harvesting.

<Voltage monitoring circuit (second embodiment)>
FIG. 8 is a diagram illustrating a second embodiment of the voltage monitoring circuit 30. The voltage monitoring circuit 30 of this embodiment includes a resistance ladder 33 and a switch 34.

  The resistor ladder 33 includes resistors 33a and 33b (resistance values R33a and R33b) connected in series between the input terminal of the input voltage Vin and the ground terminal, and the input voltage Vin from the connection node between the resistors 33a and 33b. Is a voltage dividing circuit that outputs a divided voltage Vdiv (= Vin × {R33b / (R33a + R33b)}). The divided voltage Vdiv is sent to the control unit 23 as the output signal So of the voltage monitoring circuit 30.

  The switch 34 is connected between the input terminal of the input voltage Vin and the resistance ladder 33 and is turned on / off according to an instruction from the control unit 23.

  The control unit 23 includes an A / D [analog-to-digital] converter 23a that converts the analog output signal So into a digital signal, confirms the voltage value of the divided voltage Vdiv, and the input voltage Vin is higher than the reference voltage Vref. It is determined whether or not it is too high. Further, the control unit 23 turns on the switch 34 at the timing of reading the voltage value of the divided voltage Vdiv every cycle T, and turns off the switch 34 after reading the voltage value of the divided voltage Vdiv. By such control, current does not continue to flow through the resistance ladder 33, so that wasteful current consumption can be eliminated.

  In the voltage monitoring circuit 30 of this embodiment, unlike the first embodiment (FIG. 7), even the reset IC 31 is not used, so that further area reduction can be realized. Further, in the voltage monitoring circuit 30, it is sufficient to adjust the resistance values R33a and R33b so that the divided voltage Vdiv falls within the input dynamic range of the control unit 23 while suppressing the current consumption. Simple.

  If the voltage monitoring circuit 30 of the present embodiment is used, the control unit 23 can not only obtain the comparison result between the input voltage Vin and the reference voltage Vref but also recognize the voltage value itself of the input voltage Vin. . Therefore, for example, it is possible to acquire prediction information such as how much power is insufficient for returning to the active state, and how much the sleep state should be continued. If such prediction information is notified to the manager of the sensor network X, it can be understood how many hours later the data should be read. Further, if the divided voltage Vdiv is read every period T, it can be seen how much the divided voltage Vdiv changes during the period T. Therefore, it becomes possible to grasp the current harvester capability in the energy harvesting unit 11. Further, when the change amount of the divided voltage Vdiv during the period T is smaller than a predetermined value, the timing at which the A / D converter 23a of the control unit 23 reads the divided voltage Vdiv next is k × according to the degree. It may be set to T (where k is an integer of 2 or more). By adopting such a configuration, it is not necessary to read the divided voltage Vdiv every period T, so that further reduction in power consumption can be realized.

<Sensor network (second embodiment)>
FIG. 9 is a diagram showing a second embodiment of the sensor network. The sensor network X of this embodiment is constructed as a one-to-many wireless sensor network, and the receiver 2 is shared by a plurality of sensor modules 1.

  Examples of application of such sensor network X include medical / health field (health management and safety confirmation), structure monitoring (wire breakage and bolt looseness monitoring), plant monitoring (equipment abnormality monitoring), and Distribution management (monitoring of distribution status and quality) can be mentioned.

  However, when constructing the sensor network X of the present embodiment, a collision between sensor modules 1 provided for a single receiver 2 (= collision of radio signals and associated data loss, etc.) Need to avoid. In particular, when the number of sensor modules 1 is large, the collision occurrence rate is increased, and thus a countermeasure for avoiding the collision is essential. Therefore, the collision avoidance method in the sensor network X will be specifically described below.

  FIG. 10 is a time chart showing an example of a collision avoidance method. The communication timings of a plurality (three in this figure) of sensor modules 1 (1) to 1 (3) are indicated by a circle in order from the upper side of the drawing. It is depicted.

  As shown in the figure, the communication timings of the sensor modules 1 (1) to 1 (3) are shifted from each other in order to avoid collision between each other. For example, the sensor modules 1 (1) to 1 (3) have different times t41 (1) to t41 (3), times t42 (1) to t42 (3), and times t43 (1) to t43 ( Wireless communication is performed in 3).

  For example, each of the sensor modules 1 (1) to 1 (3) may employ a collision avoidance method that performs wireless communication while shifting the timing with reference to the time of a built-in clock (RTC [real time clock] or the like). More specifically, each of the sensor modules 1 (1) to 1 (3) is provided with a transmission / reception function, and the communication timing is shifted with respect to the time of the built-in clock while taking mutual communication. Just keep it.

  As described above, the data acquisition interval (and hence the wireless communication interval) of each of the sensor modules 1 (1) to 1 (3) is the period T. Therefore, the above mutual communication does not necessarily have to be performed every time the communication timing arrives, and may be performed at least at the first communication timing. This is because if the first communication timings are shifted from each other, the second and subsequent communication timings that come every time the period T elapses are inevitably shifted as shown in this figure.

  Further, for example, in each of the sensor modules 1 (1) to 1 (3), a collision avoidance method (so-called LBT [listen before talk] is performed in which each of the sensor modules 1 (1) to 1 (3) confirms that the other sensor modules are not performing wireless communication. ], For example, an EnOcean communication protocol (ERP [enocean radio protocol] 2 in Japan, ERP1 in the United States or Europe) may be employed. More specifically, sensor modules 1 (1) to 1 (3 ) Check whether there is a terminal transmitting a radio signal around itself by picking up the radio signal as a receiver before starting transmission of the radio signal. If there is a terminal, it may be configured to wait until the terminal completes transmission of the radio signal and then start transmitting its own radio signal.

  Further, for example, each of the sensor modules 1 (1) to 1 (3) employs a collision avoidance technique (so-called TSA [time slot assign] technique) in which wireless communication is performed only in a time slot designated by a separate system manager. May be. More specifically, as shown in FIG. 11, (1) when sufficient energy required for each sensor module to operate is secured, a transmission request is issued to the receiver, and (2) reception is performed. The machine receives the transmission request and notifies the sensor module of the slot number. (3) The sensor module receives the notification of the slot number and transmits data in the designated time slot.

<Battery installed>
Since there are many applications that cannot be handled by the energy harvesting unit 11, a battery (such as a mobile battery) may be provided in parallel with the energy harvesting unit 11 to cover this. The positioning of the battery is the same as that of the energy harvesting unit 11.

  When a battery is used, power is supplied to the load while charging the power storage unit 12. The same applies to the energy harvesting unit 11. However, since the output current of the battery is quite small, the power supply source is only the power storage unit 12 as a whole. The environmental power generation unit 11 may be considered as a battery having a considerably high output impedance.

  The sleep operation described above does not depend on which of the energy harvesting unit 11 and the battery is used. The sleep operation is controlled by software. After the sleep state of the period T has elapsed, the input voltage Vin is checked, and if it exceeds the reference voltage Vref, it returns to the active state, and if it falls below, the sleep state of the period T is maintained again. Is performed in the same manner as when the energy harvesting unit 11 is used.

<Other variations>
The various technical features disclosed in the present specification can be variously modified within the scope of the technical creation in addition to the above-described embodiment. That is, the above-described embodiment should be considered as illustrative in all points and not restrictive, and the technical scope of the present invention is not limited to the above-described embodiment, and It should be understood that all modifications that fall within the meaning and range are included.

  The sensor module or sensor network disclosed in the present specification can be suitably used, for example, as a monitoring means for infrastructure equipment or FA equipment.

DESCRIPTION OF SYMBOLS 1, 1 (1) -1 (3) Sensor module 2 Receiver 3 Server 10 Power supply circuit 11 Environmental power generation part 12 Power storage part 13 Power management part 20 Sensor circuit 21 Sensor part 22 Wireless communication part 23 Control part 23a A / D converter 30 Voltage monitoring circuit 31 Reset IC
32 Pull-up resistor 33 Resistor ladder 33a, 33b Resistor 34 Switch CMP comparator N1 N-channel MOS field effect transistor X Sensor network

Claims (11)

A power supply circuit including an energy harvesting unit and a power storage unit;
A sensor circuit that receives power from the power supply circuit and operates intermittently;
A voltage monitoring circuit for constantly monitoring the input voltage stored in the power storage unit;
Have
The sensor circuit alternately repeats an active state in which measurement of a measurement target and wireless communication of a measurement result and a sleep state in which the operation is suspended. In the sleep state, the voltage monitoring is performed at a predetermined cycle. A sensor module that performs output check of the circuit and returns to the active state if the input voltage is higher than a predetermined reference voltage, and maintains the sleep state if the input voltage is lower than the reference voltage. .   The sensor module according to claim 1, wherein the power supply circuit further includes a power management unit that generates a power supply voltage from the input voltage and supplies the power supply voltage to the sensor circuit.   The voltage monitoring circuit includes a reset IC that generates a reset signal according to a comparison result between the input voltage and the reference voltage, and the sensor circuit confirms a logic level of the reset signal, and the input voltage is The sensor module according to claim 1, wherein it is determined whether or not the voltage is higher than a reference voltage.   The voltage monitoring circuit includes a resistance ladder that generates a divided voltage of the input voltage, and the sensor circuit confirms a voltage value of the divided voltage to determine whether the input voltage is higher than the reference voltage. The sensor module according to claim 1, wherein the sensor module is determined.   The sensor module according to any one of claims 1 to 4, wherein the energy source of the environmental power generation unit and the measurement target of the sensor circuit are common. The sensor module according to any one of claims 1 to 5,
A receiver for wirelessly receiving the measurement result of the sensor module;
A sensor network comprising:   The sensor network according to claim 6, further comprising a server that receives a measurement result of the sensor module from the receiver and records and analyzes the result.   The sensor network according to claim 6, wherein the receiver is shared by a plurality of sensor modules.   The sensor network according to claim 8, wherein each of the plurality of sensor modules performs wireless communication while shifting a timing with reference to a time of a built-in clock.   The sensor network according to claim 8, wherein each of the plurality of sensor modules performs wireless communication after confirming that another sensor module is not performing wireless communication.   The sensor network according to claim 8, wherein each of the plurality of sensor modules performs wireless communication in a designated time slot.