JP2018096883A - Electrostatic capacitance sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic capacitance sensor that reduces wrong detection attributed to an external factor.SOLUTION: An electrostatic capacitance sensor 100 comprises: a sensor electrode 10 in which an electrostatic capacitance varies with a distance change to an object; a control unit 40; a low-pass filter 20 that is connected between the sensor electrode 10 and the control unit 40; and a first switch 31 that switches ON/OFF of the low-pass filter 20. The control unit 40 is configured to turn on the low-pass filter 20 by the first switch 31 within a first predetermined time T1 to detect a first electrostatic capacitance being generated in the sensor electrode 10. The control unit 40 is configured to, when the first electrostatic capacitance varies equal to or greater than a first predetermined capacitance Cth0, turn off the low-pass filter 20 by the first switch 31, and detect a second electrostatic capacitance being generated in the electrode sensor 10 within a second predetermined time T2. The control unit 40 is configured to, when a fluctuation band of the second electrostatic capacitance is equal to or greater than a second predetermined capacitance Cth1, determine that an electromagnetic wave is applied to the sensor electrode 10.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a capacitance sensor that detects a relative movement of an object such as an approach.

  2. Description of the Related Art Conventionally, a capacitance sensor that detects relative movement such as approach of an object has been proposed by utilizing the fact that the capacitance of an electrode changes with a change in distance to the object. For example, Patent Document 1 discloses a capacitance sensor that detects the approach of a human body to a sensor electrode. The sensor electrode is connected to the reference capacitor and the resistor. For calculation of the capacitance of the sensor electrode, either calculation based on the charging time of the sensor electrode via the resistor or calculation based on charging / discharging of the sensor electrode via the reference capacitor is used depending on the situation. .

US Patent No. 9304156

  In the capacitance sensor described in Patent Document 1, when an electromagnetic wave due to an external factor is applied, the sensor electrode becomes an antenna, and the potential in the capacitance sensor may fluctuate. As a result, erroneous detection may occur in the capacitance sensor.

  The present disclosure provides a capacitive sensor that reduces false detections due to external factors.

  An electrostatic capacity sensor according to an aspect of the present disclosure includes an electrode whose electrostatic capacity changes due to a change in distance from an object, a control unit electrically connected to the electrode, and between the electrode and the control unit. A low-pass filter connected to the switch, and a switch that switches the low-pass filter on and off by the control unit, and the control unit turns on the low-pass filter by the switch and supplies the electrode to the electrode within a first predetermined period. When the generated first capacitance is detected and the first capacitance changes by more than a first predetermined value, the low-pass filter is turned off by the switch, and a first generated at the electrode within a second predetermined period. 2 capacitance is detected, and it is determined that an electromagnetic wave is applied to the electrode when the fluctuation range of the second capacitance is equal to or greater than a second predetermined value.

  According to the capacitance sensor of the present disclosure, it is possible to reduce false detection due to an external factor.

It is a figure which shows the notional structure of the electrostatic capacitance sensor which concerns on embodiment. It is a figure which shows an example of a specific structure of the electrostatic capacitance sensor of FIG. It is a flowchart which shows an example of the flow of the detection operation | movement by the electrostatic capacitance sensor which concerns on embodiment. It is a flowchart which shows an example of the flow of the detection operation | movement by the electrostatic capacitance sensor which concerns on embodiment. It is a flowchart which shows an example of the flow of a process which determines the capacity | capacitance conversion value of a sensor electrode. It is a graph which shows an example of change of the capacity conversion value of a sensor electrode at the time of relative movement of a subject. It is a graph which shows an example of the change of the capacity | capacitance conversion value of a sensor electrode at the time of noise mixing. It is a figure which shows the structure of the modification of the electrostatic capacitance sensor which concerns on embodiment. It is a perspective view which shows the application example of the electrostatic capacitance sensor which concerns on embodiment and a modification.

  Hereinafter, embodiments will be described with reference to the drawings. Each of the embodiments described below shows a specific example. Numerical values, shapes, materials, components, arrangement positions and connection forms of components, steps, order of steps, and the like shown in the following embodiments are merely examples, and are not intended to limit the scope of the claims. In addition, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims indicating the highest concept are described as optional constituent elements. In addition, the ordinal numbers such as the first, second, and third may be appropriately added to the components and the like in terms of expression.

  In the following description of the embodiments, expressions with “substantially” such as substantially parallel and substantially orthogonal may be used. For example, “substantially parallel” not only means completely parallel, but also means substantially parallel, that is, including a difference of, for example, several percent. The same applies to expressions involving other “abbreviations”. Each figure is a mimetic diagram and is not necessarily illustrated strictly. Furthermore, in each figure, the same code | symbol is attached | subjected to the substantially same component, and the overlapping description may be abbreviate | omitted or simplified.

[Embodiment]
[1. Capacitance sensor configuration]
With reference to FIG.1 and FIG.2, the structure of the electrostatic capacitance sensor 100 which concerns on embodiment of this indication is demonstrated. FIG. 1 is a diagram illustrating a conceptual configuration of a capacitance sensor 100 according to an embodiment. FIG. 2 is a diagram illustrating an example of a specific configuration of the capacitance sensor 100 of FIG. The electrostatic capacity sensor 100 is configured such that an object with a potential such as a human limb approaches the sensor electrode 10 of the electrostatic capacity sensor 100, the object contacts the sensor electrode 10, or in the vicinity of the sensor electrode 10. The relative movement of the object relative to the sensor electrode 10 such as the movement of the object relative to the sensor electrode 10 can be detected. The sensor electrode 10 has a capacitance and forms an electric field. When the distance between the object and the sensor electrode 10 changes due to the relative movement of the object, the electric field is affected and the capacitance of the sensor electrode 10 changes. For example, when a human body part such as a limb approaches the sensor electrode 10, the capacitance of the sensor electrode 10 increases. As described above, the capacitance sensor 100 detects the relative movement of the object based on the change in the capacitance of the sensor electrode 10 caused by the change in the distance between the object and the sensor electrode 10. The capacitance sensor 100 can detect the relative movement of the object within the electric field formed by the sensor electrode 10. Here, the sensor electrode 10 is an example of an electrode.

  Referring to FIG. 1, the capacitance sensor 100 includes a sensor electrode 10, a low-pass filter 20, a switch 31, and a control unit 40. The controller 40 is connected between a positive electrode terminal 51 to which a DC voltage V1 is applied from a DC voltage source (not shown) and a negative electrode terminal 52 to which a DC voltage V2 lower than the DC voltage V1 is applied. In the present embodiment, since the negative terminal 52 is connected to the ground, the DC voltage V2 is the ground potential. In addition, the connection of the above-mentioned control part 40 and the connection of the component demonstrated below include an electrical connection, and may be a physical direct connection or a physical indirect connection. .

  The sensor electrode 10 has a first electrode 11 and a second electrode 12 that are spaced apart from each other. The sensor electrode 10 forms a capacitor, for example, but may have any configuration including the first electrode 11 and the second electrode 12. The first electrode 11 is connected to the control unit 40, and the second electrode 12 is connected to the negative terminal 52.

  The low-pass filter 20 is connected in series between the first electrode 11 and the control unit 40, and further connected to the negative terminal 52. The switch 31 is connected to a connection point between the first electrode 11 and the low-pass filter 20 and a connection point between the low-pass filter 20 and the control unit 40. That is, the switch 31 is connected in parallel with the low-pass filter 20 with respect to the first electrode 11 and the control unit 40. The switch 31 selectively turns on and off the low pass filter 20. That is, the switch 31 switches between transmitting a signal from the sensor electrode 10 to the control unit 40 via the low-pass filter 20 and transmitting the signal without passing through the low-pass filter 20.

  The control unit 40 controls the current output from the control unit 40 to the sensor electrode 10, controls the on / off operation of the switch 31, and detects the capacitance of the sensor electrode 10. In the capacitance sensor 100 configured as described above, the sensor electrode 10 and the control unit 40 are connected via the low-pass filter 20 and the low-pass filter 20 in accordance with the on / off operation of the switch 31. Selected from with no connection. The control unit 40 detects the capacitance of the sensor electrode 10 while switching the on state and off state of the switch 31. Details of the capacitance detection process of the sensor electrode 10 will be described later.

  Referring to FIG. 2, an example of a specific circuit configuration of the capacitance sensor 100 is shown. The sensor electrode 10 has a first electrode 11 and a second electrode 12. Low pass filter 20 includes an impedance element 21 and a reference capacitor 22. In the present embodiment, the impedance element 21 is a resistor, but may be an inductor. The control unit 40 includes a constant current source 60, a comparator 70, a processing unit 80, switches 32 and 33, a first memory 91, a second memory 92, a third memory 93, and a timer 94. ing. The constant current source 60, the first memory 91, the second memory 92, the third memory 93, and the timer 94 may be provided in, for example, a device on which the capacitance sensor 100 is mounted. Hereinafter, the switch 31 is referred to as a first switch, and the switches 32 and 33 are referred to as a second switch and a third switch, respectively.

  The constant current source 60 is constituted by a constant current circuit, for example. The constant current source 60 outputs a current from the positive terminal 51 with a constant value. The constant current source 60 is connected to the positive terminal 51 and further connected to the first electrode 11 of the sensor electrode 10. The impedance element 21 is connected in series between the constant current source 60 and the first electrode 11.

  The second switch 32 is connected in series between the constant current source 60 and the impedance element 21. That is, the constant current source 60, the second switch 32, the impedance element 21, and the sensor electrode 10 are connected in series in this order. The second switch 32 selectively turns on and off the current flow from the constant current source 60 to the impedance element 21.

  The third switch 33 is connected to a connection point between the second switch 32 and the impedance element 21, and further connected to the negative terminal 52. The third switch 33 selectively turns on and off the flow of current from the connection point between the second switch 32 and the impedance element 21 to the negative terminal 52.

  The first switch 31 is connected to a connection point between the first electrode 11 of the sensor electrode 10 and the impedance element 21, and further connected to a connection point between the impedance element 21 and the second switch 32. In the present embodiment, the first switch 31 is directly connected to both ends of the impedance element 21, but is not limited to this.

  The reference capacitor 22 is connected to the connection point between the constant current source 60 and the second switch 32, and is further connected to the negative terminal 52.

  The timer 94 is configured to operate under the control of the processing unit 80. The timer 94 measures time related to the processing of the processing unit 80 and sends the measured time to the processing unit 80.

  The comparator 70 compares the reference voltage Vref and the output DC voltage Vc, and outputs an output signal indicating the comparison result to the processing unit 80. A non-inverting input terminal (+ terminal in FIG. 2) of the comparator 70 is connected to a connection point between the constant current source 60 and the second switch 32. The output DC voltage Vc is an output DC voltage from the constant current source 60 and is also a voltage applied to the sensor electrode 10. The inverting input terminal (-terminal in FIG. 2) of the comparator 70 is connected to a reference voltage circuit (not shown) that outputs the reference voltage Vref.

  The processing unit 80 controls the on / off operation of the first switch 31, the second switch 32, and the third switch 33. Further, the processing unit 80 receives an output signal indicating the comparison result from the comparator 70, and detects the capacitance of the sensor electrode 10 using the received output signal. The processing unit 80 may be configured by a computer system (not shown) including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read-Only Memory), and the like. A part or all of the functions of the processing unit 80 may be achieved by the CPU executing a program recorded in the ROM using the RAM as a working memory. Further, some or all of the functions of the processing unit 80 may be achieved by a dedicated hardware circuit. Note that the processing unit 80 may be configured by a single component that performs centralized control, or may be configured by a plurality of components that perform distributed control in cooperation with each other.

  Each of the first memory 91 to the third memory 93 receives information from the processing unit 80 and stores it. Further, each of the first memory 91 to the third memory 93 is configured such that stored information is pulled out by the processing unit 80. For example, each of the first memory 91 to the third memory 93 stores and stores the capacitance value of the sensor electrode 10 detected by the processing unit 80. Each of the first memory 91 to the third memory 93 may be realized by, for example, a semiconductor memory or a hard disk drive. Each of the first memory 91 to the third memory 93 may be a volatile memory or a nonvolatile memory.

[2. Operation of capacitance sensor]
Hereinafter, the operation of the capacitance sensor 100 shown in FIG. 2 will be described with reference to FIGS. 2, 3A, 3B, and 4. FIG. 3A and 3B are flowcharts illustrating an example of a flow of detection operation by the capacitance sensor 100 according to the embodiment. FIG. 4 is a flowchart illustrating an example of a process flow for determining the capacitance conversion value of the sensor electrode 10.

  As shown in FIGS. 3A and 3B, when the capacitance sensor 100 is activated, the processing unit 80 opens or turns off the first switch 31 (step S101). At this time, the processing unit 80 places the second switch 32 in a closed state, that is, an on state, and sets the third switch 33 in an open state, that is, an off state. Thereby, the current from the constant current source 60 flows to the sensor electrode 10 through the impedance element 21 without detouring to the first switch 31 and the third switch 33.

  Next, the processing unit 80 performs a capacitance detection process for the sensor electrode 10 within a predetermined period, that is, the first predetermined time T1 (step S102). Although details will be described later, the processing unit 80 performs a process of determining a capacitance converted value of the capacitance of the sensor electrode 10 every time the first predetermined time T1 elapses. In other words, the processing unit 80 repeats the process of determining the capacity conversion value within the first predetermined time T1. The timer 94 performs the time measurement of the first predetermined time T1. In the present embodiment, the first predetermined time T1 is a period depending on the moving speed with respect to the sensor electrode 10 assumed for the object. The first predetermined time T1 is a length that allows the relative movement of the object during the time T1 to be reflected in the change in the capacitance of the sensor electrode 10, and 50 msec (milliseconds) is taken as an example. It is done. Then, the processing unit 80 stores the determined capacity conversion value C1 in the first memory 91 (step S103). The first predetermined time T1 is an example of a first predetermined period.

  Here, with reference to FIG. 4, a process in which the processing unit 80 determines the capacitance converted value of the sensor electrode 10 will be described. When starting the confirmation process, the processing unit 80 first stops the constant current source 60 (step S201). Thereby, the output of the current from the constant current source 60 is stopped. Next, the processing unit 80 performs an operation of simultaneously closing the second switch 32 and the third switch 33 (step S202). At this time, the first switch 31 is maintained in a state immediately before the confirmation process is started. For example, after step S101, the first switch 31 is maintained in the open state. Since the second switch 32 and the third switch 33 are closed, the potential difference between the sensor electrode 10 and the reference capacitor 22 becomes zero, and the capacitances of the sensor electrode 10 and the reference capacitor 22 are initialized to zero. Thereafter, the processing unit 80 performs an operation of opening the second switch 32 and the third switch 33 at the same time (step S203), and then starts the constant current source 60 (step S204).

  After activation of the constant current source 60, the processing unit 80 alternately repeats the opening operation and the closing operation for the second switch 32 and the third switch 33 (step S205). That is, a state where one of the second switch 32 and the third switch 33 is opened and the other is closed and a state where one is closed and the other is opened are alternately repeated. As a result, when the second switch 32 is closed and the third switch 33 is opened, charge is accumulated in the sensor electrode 10. Here, since the electrostatic capacity of the sensor electrode 10 is smaller than the electrostatic capacity of the reference capacitor 22, electric charges are steeply accumulated in the sensor electrode 10 until the voltage of the reference capacitor 22 (output DC voltage Vc) is reached. . On the other hand, the reference capacitor 22 accumulates charges more slowly than the sensor electrode 10. When the second switch 32 is opened and the third switch 33 is closed, the charge stored in the sensor electrode 10 is discharged.

  By repeating the above operation, if the capacitance of the sensor electrode 10 is large, that is, if the object is close, a large amount of electric charge is accumulated in the sensor electrode 10. Less charge is accumulated. Therefore, the time (charge time) until the voltage of the reference capacitor 22 (output DC voltage Vc) reaches the reference voltage Vref becomes longer. For this reason, if the charging time when the output DC voltage Vc exceeds the reference voltage Vref is measured, the capacitance of the sensor electrode 10 can be estimated, in other words, the proximity of the object can be detected.

  By such an operation, the processing unit 80 calculates a capacitance converted value of the sensor electrode 10 based on the detection result of the output DC voltage Vc by the comparator 70. Specifically, the comparator 70 determines whether or not the output DC voltage Vc exceeds the reference voltage Vref, that is, whether Vc> Vref is satisfied (step S206). If Vc> Vref, the comparator 70 outputs a signal to the processing unit 80, whereby the processing unit 80 recognizes that Vc> Vref (Yes in step S206), and proceeds to the processing of step S207. move on. If Vc> Vref is not satisfied, the comparator 70 does not output a signal, so the processing unit 80 recognizes that the output DC voltage Vc> reference voltage Vref is not satisfied (No in step S206), and returns to step S205.

  The processing unit 80 that has received the signal from the comparator 70 is a capacitance converted value that is an estimated capacitance of the sensor electrode 10 based on a charging time that is an elapsed time from when the constant current source 60 starts up until Vc> Vref. C is estimated (step S207).

  Note that the estimated capacitance of the sensor electrode 10 is proportional to the charging time. For example, when an object exists in the vicinity of the sensor electrode 10 or in contact with the sensor electrode 10, the capacitance of the sensor electrode 10 increases. Thereby, the charging current from the constant current source 60 to the sensor electrode 10 increases, but the charging current from the constant current source 60 to the reference capacitor 22 decreases. Therefore, the charging time of the reference capacitor 22 becomes long. On the other hand, when there is no object in the vicinity of the sensor electrode 10, the capacitance of the sensor electrode 10 becomes small, so that the charging current from the constant current source 60 to the sensor electrode 10 becomes small and the constant current source 60 to the reference capacitor 22. The charging current to becomes larger. Therefore, the charging time of the reference capacitor 22 is shortened.

  Through the processes in steps S201 to S207 as described above, the capacitance converted value of the sensor electrode 10 is calculated after the capacitance is once initialized.

  3A and 3B, if the first predetermined time T1 has elapsed after the opening operation of the first switch 31 in step S101 (Yes in step S104), the processing unit 80 converts the capacitance of the sensor electrode 10 into a capacitance. A process of newly calculating and determining a value is performed (step S105). When the first predetermined time T1 has not elapsed (No in step S104), the processing unit 80 repeats the elapsed time determination process (step S104).

  In step S105, the processing unit 80 newly determines a capacitance converted value C2 of the sensor electrode 10 by the processing in steps S201 to S207 described above. Then, the processing unit 80 stores the determined new capacity conversion value C2 in the second memory 92 (step S106). Next, the processing unit 80 compares the capacity conversion value C2 with the capacity conversion value C1 determined in the capacity conversion value determination process immediately before the capacity conversion value C2 determination process. Specifically, the processing unit 80 determines whether or not the absolute value | C2-C1 | of C2-C1, which is the difference between the converted capacity value C2 and the converted capacity value C1, is equal to or greater than the first predetermined capacity Cth0. (Step S107). Here, the first predetermined capacity Cth0 is an example of a first predetermined value.

  | C2-C1 | may reflect the relative speed of the object with respect to the sensor electrode 10. For example, if the relative speed of the object approaching the sensor electrode 10 increases, | C2-C1 | increases. However, when | C2-C1 | is a large value that is equal to or greater than the threshold value, | C2-C1 | does not reflect the relative speed of the object, but reflects the influence of disturbances such as noise having a relatively high frequency. There is a possibility. In the present embodiment, the first predetermined capacity Cth0 is set as such a threshold value.

  When | C2-C1 | <Cth0 (No in step S107), the processing unit 80 determines the presence / absence of the relative movement of the object with respect to the sensor electrode 10 and the content thereof based on the converted capacitance values C1 and C2 ( Step S109). The processing unit 80 does not detect the relative movement of the object when | C2-C1 | is approximately zero, but detects the relative movement of the object when | C2-C1 | is not approximately zero. Can do. Further, the processing unit 80 can determine the type of relative movement of the object such as approach or movement based on a change in the value of | C2-C1 | calculated every first predetermined time T1. Details of the determination of the relative movement type will be described later. Then, the processing unit 80 outputs the determination result as a signal or the like. Note that the state in which | C2-C1 | is substantially zero means that the capacitance conversion value has changed in consideration of the change in the capacitance conversion value due to the environmental change such as the state of the air around the sensor electrode 10. It means a state that can be regarded as not.

  Next, the processing unit 80 stores the data stored in the second memory 92 in the first memory 91 (step S110). Thereby, the capacity | capacitance conversion value C2 is stored in the 1st memory 91 as the new capacity | capacitance conversion value C1. In the first memory 91, the past capacity conversion value C1 may be updated with a new capacity conversion value C1, or may be left. Thereafter, the processing unit 80 continues the operation after step S104.

  When | C2-C1 | ≧ Cth0 (Yes in Step S107), the processing unit 80 closes the first switch 31 (Step S108). At this time, the processing unit 80 closes the second switch 32 and also opens the third switch 33. As a result, the current from the constant current source 60 bypasses the impedance element 21 and flows to the sensor electrode 10 through the first switch 31.

  Next, the processing unit 80 performs a process of determining the converted capacitance value of the sensor electrode 10 within a predetermined period, that is, the second predetermined time T2 (step S111). Although details will be described later, the processing unit 80 performs a process of determining a capacitance converted value of the sensor electrode 10 every second predetermined time T2 that is different from the first predetermined time T1. In other words, the processing unit 80 repeats the process of determining the capacity conversion value within the second predetermined time T2. In the present embodiment, the second predetermined time T2 is a period that depends on the period of the electromagnetic wave due to noise or the like that is a disturbance other than the object acting on the sensor electrode 10. Such electromagnetic waves have a relatively high frequency. The second predetermined time T2 is a length that allows the influence of electromagnetic waves to be reflected in the fluctuation of the capacitance of the sensor electrode 10 determined every time T2, and 5 msec (milliseconds) is an example. Thus, in the present embodiment, the second predetermined time T2 is significantly smaller than the first predetermined time T1. Then, the processing unit 80 stores the capacity conversion value Cnk (k = 1, 2,..., N) determined every second predetermined time T2 in the third memory 93 (step S112). The third memory 93 includes a plurality of memories Rnk (k = 1, 2,..., M). Note that m ≧ n. Each of the plurality of converted capacitance values Cnk is stored in one memory Rnk. Here, the second predetermined time T2 is an example of a second predetermined period.

  If the second predetermined time T2 has elapsed after the processing unit 80 has started the process of step S111 for the first time, or has recently counted the second predetermined time T2 (Yes in step S113), the processing unit 80 The process proceeds to S114. When the second predetermined time T2 has not elapsed (No in step S113), the processing unit 80 repeats the elapsed time determination process (step S113).

  Furthermore, if the first predetermined time T1 has elapsed after starting the process of step S111 for the first time in step S114 (Yes in step S114), the processing unit 80 proceeds to the process of step S115. When the first predetermined time T1 has not elapsed (No in step S114), the processing unit 80 returns to step S111 and performs a process of determining a new capacitance conversion value Cnk of the sensor electrode 10. As described above, by repeating the processes of S111 to S114, a plurality of converted capacity values Cnk (k = 1, 2,..., N) are sequentially stored in the plurality of memories Rnk of the third memory 93. The And the repetition of the process of S111-S114 is performed over 1st predetermined time T1.

  In step S115, the processing unit 80 extracts the maximum value Cmax and the minimum value Cmin from the plurality of capacity conversion values Cnk stored in the plurality of memories Rnk. Further, the processing unit 80 determines whether or not the absolute value | Cmax−Cmin | of Cmax−Cmin, which is the difference between the maximum value Cmax and the minimum value Cmin, is equal to or greater than the second predetermined capacity Cth1 (step S116). . That is, the processing unit 80 determines whether or not the fluctuation range of the capacity conversion value Cnk within the first predetermined time T1, specifically, the maximum fluctuation range is equal to or greater than the second predetermined capacity Cth1. Here, the second predetermined capacity Cth1 is an example of a second predetermined value.

  Regarding the fluctuation range of the capacitance conversion value Cnk, the fluctuation range of the capacitance conversion value caused by electromagnetic waves due to noise or the like is larger than the fluctuation range of the capacitance conversion value caused by the relative movement of the object with respect to the sensor electrode 10. growing. For this reason, when the fluctuation range of the capacitance conversion value Cnk is a large value that is equal to or larger than the threshold value, the fluctuation range is more likely to be caused by electromagnetic waves. In the present embodiment, the second predetermined capacity Cth1 is set as such a threshold value. In particular, by using | Cmax−Cmin |, evaluation of the fluctuation range of the capacity conversion value Cnk becomes efficient.

  When | Cmax−Cmin | ≧ Cth1 (Yes in Step S116), the processing unit 80 determines that an electromagnetic wave such as noise due to disturbance is applied to the sensor electrode 10, and sets a disturbance noise flag (Step S117). Thereafter, the processing unit 80 opens the first switch 31 (step S118). Next, the processing unit 80 recognizes that the capacitance determination value of the detected sensor electrode 10 includes a disturbance in a state where the low-pass filter 20 including the impedance element 21 and the reference capacitor 22 is turned on. You may perform the process which detects the relative movement of an object. In addition, the processing unit 80 may return to step S104 to detect the converted capacitance value of the sensor electrode 10 for each first predetermined time T1, and return to step S108 to perform the second predetermined time within the first predetermined time T1. The capacitance conversion value of the sensor electrode 10 may be detected every time T2. Further, the processing unit 80 may remove noise using a filter. Alternatively, the processing unit 80 may interrupt the process for detecting the relative movement of the object.

  When | Cmax−Cmin | <Cth1 (No in step S116), the processing unit 80 determines that no electromagnetic wave is applied to the sensor electrode 10, and stores the data stored in the second memory 92 in the first memory 91. (Step S119). Thereby, the capacity conversion value C2 stored in the second memory 92 is stored in the first memory 91 as a new capacity conversion value C1. The processing unit 80 may store in the first memory 91 at least one of the plurality of converted capacity values Cnk stored in the third memory 93 as a new converted capacity value C1. The stored capacity conversion value may be one of the plurality of capacity conversion values Cnk, for example, the capacity conversion value Cnk calculated last. Or the capacity | capacitance conversion value stored may be calculated by statistical calculation with respect to several capacity | capacitance conversion value Cnk. For example, the stored capacity conversion values may be representative values such as various average values, median values, mode values, maximum values, and minimum values of the plurality of capacity conversion values Cnk.

  Subsequent to step S119, the processing unit 80 opens the first switch 31 (step S120). And the process part 80 performs the process which detects the relative movement of a target object in the state which turned on the low-pass filter 20 by the impedance element 21 and the reference | standard capacitor | condenser 22. FIG. Specifically, the processing unit 80 performs a process of detecting a new capacitance conversion value C2 of the sensor electrode 10 (step S121). Next, the processing unit 80 stores the detected new converted capacity value C2 in the second memory 92 (step S122), and based on the converted capacity value C1 of the first memory 91 and the converted capacity value C2 of the second memory 92. The presence / absence of the relative movement of the object with respect to the sensor electrode 10 and the content thereof are determined (step S123). Note that the processing unit 80 does not detect the relative movement of the object when C2-C1 is substantially zero, but does not detect the relative movement of the object when C2-C1 is not substantially zero, as in step S109. Can be detected. Furthermore, the processing unit 80 can determine the type of relative movement of the object based on a change in the value of C2-C1 calculated every first predetermined time T1. Then, the processing unit 80 outputs the determination result as a signal or the like.

  Next, the processing unit 80 stores the data stored in the second memory 92 in the first memory 91 (step S124). Thereby, the capacity | capacitance conversion value C2 is stored in the 1st memory 91 as the new capacity | capacitance conversion value C1. Thereafter, the processing unit 80 returns to step S104 to detect a capacitance converted value of the sensor electrode 10 at each first predetermined time T1.

  Here, with reference to FIG. 5, details of processing in which the processing unit 80 determines the type of relative movement of the object in steps S109 and S123 will be described. FIG. 5 is a graph showing an example of a change in the capacitance converted value of the sensor electrode 10 when the object is relatively moved. FIG. 5 shows an example of a change in the capacity conversion value when an artificial operation with a human finger or the like is applied to the sensor electrode 10 as the relative movement of the object. In FIG. 5, the vertical axis represents the capacity conversion value, and the horizontal axis represents time (unit: ms [milliseconds]). In FIG. 5, the capacitance converted values of the sensor electrode 10 detected at the first predetermined time T1 are plotted over time, and the plotted points are connected by a line.

  For example, since the capacitance conversion value is substantially constant between the times ta and tb, the processing unit 80 determines that there is no relative movement of the object with respect to the sensor electrode 10. That is, the processing unit 80 determines that the zeroth artificial operation is acting on the sensor electrode 10.

  At time tc when time T1 has elapsed from time tb, the difference | Ctc−Ctb | between the converted capacity value Ctb at time tb and the converted capacity value Ctc at time tc exceeds the predetermined value A (A> 0). That is, | Ctc−Ctb |> A. For this reason, the processing unit 80 determines that there is a relative movement of the object with respect to the sensor electrode 10, and specifically, the artificial operation acting on the sensor electrode 10 is changed from the zeroth artificial operation to the first artificial operation. It is determined that the operation has been shifted.

  At time td when time T1 has elapsed from time tc, the difference | Ctd−Ctc | between the capacity conversion value Ctc and the capacity conversion value Ctd at time td exceeds the predetermined value B (B> 0). That is, | Ctd−Ctc |> B. Therefore, the processing unit 80 determines that the artificial operation acting on the sensor electrode 10 has shifted from the first artificial operation to the second artificial operation.

  At time te when time T1 has elapsed from time td, the difference | Cte−Ctd | between the converted capacity value Ctd and the converted capacity value Cte at time te exceeds the predetermined value C (C> 0). That is, | Cte−Ctd |> C. For this reason, the processing unit 80 determines that the artificial operation acting on the sensor electrode 10 has shifted from the second artificial operation to the third artificial operation.

  At the time tf when the time T1 has elapsed from the time te, the difference | Ctf−Cte | between the converted capacity value Cte and the converted capacity value Ctf at the time tf is lower than the predetermined value D (D> 0). That is, | Ctf−Cte | <D. For this reason, the processing unit 80 determines that the artificial operation acting on the sensor electrode 10 has shifted from the third artificial operation to the fourth artificial operation.

  Based on the combination and order of the zeroth artificial operation to the fourth artificial operation, the processing unit 80 can perform any series of relative movements by any artificial operation such as touch, flick, swipe, slide, and erroneous contact. Determine if there is. Thereby, the false detection of the artificial operation by the processing unit 80 is reduced. The number of artificial operations used for determination by the processing unit 80 is not limited to five as described above, and may be any number. Furthermore, the default value set for each artificial operation can be arbitrarily set according to the artificial operation.

  Next, a specific application example of the processing of steps S107 to S117 will be described with reference to FIG. FIG. 6 is a graph showing an example of a change in capacitance converted value of the sensor electrode 10 when noise is mixed. In FIG. 6, the vertical axis represents the capacity conversion value, and the horizontal axis represents time (unit: ms). In FIG. 6, the capacitance converted values of the sensor electrode 10 detected at each first predetermined time T1 are plotted with time, and the continuous change of the capacitance converted value is drawn with a line. The example of FIG. 6 shows a state where there is no relative movement of the object with respect to the sensor electrode 10.

  As shown in FIG. 6, the capacitance conversion value is substantially constant between times t <b> 0 and t <b> 1, and noise does not act on the sensor electrode 10. After time t1, noise acts on the sensor electrode 10, and the capacitance conversion value of the sensor electrode 10 greatly fluctuates in a short cycle. Usually, the processing unit 80 is in a state where the low-pass filter 20 including the impedance element 21 and the reference capacitor 22 is on, and the time t1 + T1, t1 + 2T1,..., T1 + kT1,. (K = 1, 2,...), The capacitance converted value of the sensor electrode 10 is detected. The detection result when the capacitance conversion value is detected in a state where the low-pass filter 20 is on is indicated by the plotted points in FIG.

For example, due to the mixing of noise, a difference occurs between the converted capacitance value C _t1 (first capacitance) at time t1 and the converted capacitance value C _t2 (first capacitance) at time t1 + T1. 80 may erroneously determine that there is a relative movement of the object with respect to the sensor electrode 10. Therefore, when the difference | C _t2 −C _t1 | (change in the first capacitance) is equal to or larger than the first predetermined capacitance Cth0 (first predetermined value), the processing unit 80 determines that the difference is relative to the object. It is determined whether it is caused by a simple movement or noise. For example, in the case of | C _t2 −C _t1 | ≧ Cth0, the relative speed of the object with respect to the sensor electrode 10 is equal to or higher than the assumed relative speed, and thus the difference in the capacity conversion value does not result from the relative movement of the object. there is a possibility. The first predetermined capacity Cth0 is a value equal to or greater than the predetermined values A to D related to the artificial operation described in the description of FIG.

  In order to make the above determination, the processing unit 80 closes the first switch 31 at time t1 + T1 to turn off the low-pass filter 20, and within the first predetermined time T1 from time t1 + T1 to time t1 + 2T1, The capacitance conversion value (second capacitance) of the sensor electrode 10 is detected at every second predetermined time T2 different from the time T1. Then, at time t1 + 2T1, the processing unit 80 opens the first switch 31 to turn on the low-pass filter 20. Since noise has a relatively high frequency, when the low-pass filter 20 is in an OFF state, a capacitance conversion value including the influence of noise is detected. Note that, as described above, the second predetermined time T2 is set to a length at which the influence of the electromagnetic wave can be reflected in the fluctuation of the capacitance conversion value detected every time T2. For example, the second predetermined time T2 is set corresponding to the frequency of the electromagnetic wave due to noise, and more specifically, may be set to a length that is significantly shorter than the period of the electromagnetic wave such as a quarter period.

  The processing unit 80 extracts the maximum value Cmax and the minimum value Cmin from the capacity conversion values detected every second predetermined time T2 within the first predetermined time T1. Further, when the difference | Cmax−Cmin | (variation width of the second capacitance) between the maximum value Cmax and the minimum value Cmin is equal to or greater than the second predetermined capacitance Cth1 (second predetermined value), the processing unit 80 determines this difference. Is attributed to noise. That is, when the maximum fluctuation range of the capacitance conversion value is equal to or larger than the second predetermined capacitance Cth1, it is considered that the sensor electrode 10 is affected by electromagnetic waves due to noise.

  By detecting the capacity conversion value at every second predetermined time T2, a change in the capacity conversion value at a short cycle that cannot be obtained by detection at the first predetermined time T1 is detected. For this reason, the determination accuracy of whether or not the change in the capacity conversion value is caused by noise increases.

[3. Effect]
As described above, the capacitance sensor 100 according to the embodiment includes the sensor electrode 10 whose capacitance changes due to a change in the distance to the object, the control unit 40 electrically connected to the sensor electrode 10, A low-pass filter 20 connected between the sensor electrode 10 and the control unit 40 and a first switch 31 for switching the low-pass filter 20 on and off by the control unit 40 are provided. The controller 40 turns on the low-pass filter 20 by the first switch 31 and detects the first capacitance generated in the sensor electrode 10 within the first predetermined time T1 as the first predetermined period. The control unit 40 turns off the low-pass filter 20 by the first switch 31 when the first capacitance changes by the first predetermined capacitance Cth0 as the first predetermined value, and the second predetermined time as the second predetermined period. A second capacitance generated in the sensor electrode 10 is detected within T2. The control unit 40 determines that the electromagnetic wave is applied to the sensor electrode 10 when the fluctuation range of the second capacitance is equal to or greater than the second predetermined capacitance Cth1 as the second predetermined value.

  In the above-described configuration, the capacitance of the sensor electrode 10 (first capacitance) with a shorter cycle than the variation in capacitance caused by the relative movement of the object due to the electromagnetic wave applied to the sensor electrode 10. Fluctuates. When the first capacitance changes by more than the first predetermined capacitance Cth0, that is, when there is a possibility that there is an abnormality in the change of the first capacitance, the low-pass filter 20 is turned off, and the electrostatic capacitance caused by electromagnetic waves Capacitance variations will not be removed. In this state, by detecting a capacitance (second capacitance) using a second predetermined time T2 that is different from the first predetermined time T1, it is possible to detect fluctuations in the second capacitance caused by electromagnetic waves. become. Then, by comparing the variation width of the second capacitance with the second predetermined capacitance Cth1, it is possible to identify the variation of the second capacitance as a variation caused by electromagnetic waves. Therefore, the capacitance sensor 100 can reduce erroneous detection of relative movement of the object due to external factors. Further, when the low-pass filter 20 is in the ON state, a signal from which the high frequency component has been removed is input from the sensor electrode 10 to the control unit 40, so that a change in the capacitance of the sensor electrode 10 in a short cycle can be suppressed. . Moreover, the fluctuation cycle of the electrostatic capacitance caused by the relative movement of the object with respect to the sensor electrode 10 is also relatively long. Thereby, the detection period of a capacitance can be lengthened, and the power consumption of the capacitance sensor 100 can be suppressed.

  In the capacitance sensor 100 according to the embodiment, the first predetermined time T1 is longer than the second predetermined time T2. In the above-described configuration, detecting the second capacitance within the second predetermined time T2 detects the capacitance in a shorter cycle than detecting the first capacitance within the first predetermined capacitance Cth0. Is possible. Thereby, when the electromagnetic wave acts on the sensor electrode 10, the influence of the electromagnetic wave tends to appear on the detected second capacitance.

  In the capacitance sensor 100 according to the embodiment, the first predetermined time T1 is a period corresponding to the moving speed of the object relative to the sensor electrode 10, and the second predetermined time T2 corresponds to the period of the electromagnetic wave. It is a period. In the above-described configuration, detection of the first capacitance of the sensor electrode 10 within the first predetermined time T1 can be made suitable for detection of relative movement of the object, and within the second predetermined time T2. The detection of the second capacitance of the sensor electrode 10 can be made suitable for detection of application of electromagnetic waves.

  In the electrostatic capacitance sensor 100 according to the embodiment, the control unit 40 repeatedly detects the second electrostatic capacitance of the sensor electrode 10 within the second predetermined time T2, and the second static at a different second predetermined time T2. The fluctuation range between the electric capacities is compared with the second predetermined capacity Cth1. In the above-described configuration, it is possible to accurately compare the variation in the second electrostatic capacitance of the sensor electrode 10 with the second predetermined time T2 as a cycle and the second predetermined capacitance Cth1.

  Furthermore, in the capacitance sensor 100 according to the embodiment, the control unit 40 sets the maximum value of the fluctuation range between the second capacitances of the sensor electrodes 10 at different second predetermined times T2 in the second period. Compare with the predetermined capacity Cth1. With the above-described configuration, it is possible to specify with higher accuracy whether the capacitance variation of the sensor electrode 10 is caused by electromagnetic waves or something other than electromagnetic waves. In addition, although the said predetermined period is 1st predetermined time T1 in embodiment, it is not limited to this, You may set arbitrarily.

  Further, in the capacitance sensor 100 according to the embodiment, the control unit 40 repeatedly detects the first capacitance of the sensor electrode 10 within the first predetermined time T1, and the first static time at a different first predetermined time T1. The amount of change between the capacities is compared with the first predetermined capacity Cth0. With the above-described configuration, the change in the capacitance of the sensor electrode 10 can be accurately detected.

  In the capacitance sensor 100 according to the embodiment, the low-pass filter 20 includes an impedance element 21 as a resistor, and the first switch 31 is electrically connected to both ends of the impedance element 21. In the above configuration, the first switch 31 allows the signal from the sensor electrode 10 to flow through the impedance element 21 to the control unit 40 in the off state, and the signal bypasses the impedance element 21 in the on state. The flow to the control unit 40 through the first switch 31 is allowed. Therefore, the low-pass filter 20 can be turned on / off by the first switch 31 with a simple circuit configuration.

  Furthermore, in the capacitance sensor 100 according to the embodiment, the first switch 31 is directly connected to both ends of the impedance element 21 as a resistor. With the above configuration, the impedance element 21 is short-circuited, so that the time constant of the low-pass filter 20 when the impedance element 21 is connected can be minimized. As a result, the influence of electromagnetic waves can be detected in the maximum frequency band.

[Modification]
Next, a modification of the capacitance sensor according to the embodiment will be described. Hereinafter, this modified example will be described with a focus on differences from the embodiment with reference to FIG. FIG. 7 is a view showing the configuration of a modification of the capacitance sensor according to the embodiment in the same manner as FIG.

  The capacitance sensor 200 according to the modification includes the impedance element 21 that the capacitance sensor 100 according to the embodiment includes as a resistor as an inductor. Furthermore, the capacitance sensor 200 includes a resistor 221 connected to a connection point between the impedance element 21 and the third switch 33. In this example, the resistor 221 is connected to the connection point of the impedance element 21, the third switch 33, and the second switch 32, but is not limited thereto. The resistor 221 is also connected to the negative terminal 52. Thereby, the impedance element 21 and the resistor 221 can function as a low-pass filter. Further, the impedance element 21 and the reference capacitor 22 constitute a low-pass filter 20.

  For example, when detecting the converted capacitance value of the sensor electrode 10 by the processing unit 80 of the control unit 40, when the second switch 32 and the third switch 33 are alternately opened and closed, the impedance element 21, the reference capacitor 22, and The resistor 221 removes high frequency components such as noise from the signal output from the sensor electrode 10. Therefore, even in the circuit configuration of the low-pass filter 20 different from the embodiment, noise in the sensor electrode 10 is reduced. Further, according to the capacitance sensor 200 according to the present modification, the same effect as that of the capacitance sensor 100 according to the embodiment can be obtained. The circuit constituting the capacitance sensor is not limited to this modification and the embodiment, and various circuits including the sensor electrode 10, the low-pass filter 20, the switch 31, and the control unit 40 can be applied. .

  In the configuration of FIG. 7, a fourth switch (not shown) may be provided between the connection points of the resistor 221 and the impedance element 21 and the third switch 33. In this case, the control unit 40 performs the on / off operation of the fourth switch so as to reverse the on / off of the first switch 31. Thereby, when the low-pass filter 20 is not functioned, that is, when the first switch 31 is on, the fourth switch is turned off, so that the resistor 221 is disconnected. As a result, it is possible to detect the application of a higher frequency electromagnetic wave.

[Application example of capacitance sensor]
The capacitance sensor according to the above-described embodiment and modification can detect the relative movement of the object regardless of whether the object is in contact with the capacitance sensor or not. For example, as shown in FIG. 8, the capacitance sensor according to the embodiment and the modification can be applied to a sensor that detects contact and movement of a human finger. FIG. 8 is a perspective view showing an application example of the capacitance sensor according to the embodiment and the modification. The capacitance sensor is embedded in the substrate S that comes into contact with human fingers. Specifically, the first electrode 11 and the second electrode 12 of the sensor electrode 10 of the capacitance sensor are embedded in the substrate S, and are further arranged along the surface of the substrate S at intervals from each other. The The contact of the human finger with the substrate S, the movement of the human finger on the substrate S, and the like can be detected by the capacitance sensor via the sensor electrode 10.

  In addition, the capacitance sensor according to the embodiment and the modification may be used for controlling opening / closing of a door, a rear gate and the like of a vehicle. For example, when a person inserts a foot under a door, a rear gate, or the like, that is, a lower part of the vehicle, the capacitance sensor may detect the approaching and moving direction of the foot and unlock and open the door, the rear gate, etc. . In this case, the capacitance sensor can detect the approach and movement of the foot in a non-contact state with the foot. Such a capacitance sensor can function as a switch. The capacitance sensor can be applied to any application for detecting the approach and movement of a human body part.

[Other variations]
As described above, the capacitive sensor according to one or more aspects has been described based on the embodiment as an example of the technique disclosed in the present application. However, the technology in the present disclosure is not limited to the embodiment, and can be applied to a modified example of the embodiment in which modifications, replacements, additions, omissions, and the like are appropriately performed, or other embodiments. . Unless it deviates from the gist of the present disclosure, various modifications conceived by those skilled in the art have been made in this embodiment, and forms constructed by combining components in different embodiments are also within the scope of one or more aspects. May be included.

  For example, in the capacitance sensor according to the above-described embodiment and modification, the processing unit 80 of the control unit 40 calculates the amount of change in the capacitance conversion value of the sensor electrode 10 determined every first predetermined time T1. The difference | C2-C1 | between the newly determined capacity conversion value C2 and the capacity conversion value C1 determined in the capacity conversion value determination process immediately before the capacity conversion value C2 determination process was calculated. However, it is not limited to this. For example, the processing unit 80 may calculate the difference between the capacity conversion value C2 and the capacity conversion value determined in the capacity conversion value determination process two or more times before the capacity conversion value C2 determination process. Alternatively, the processing unit 80 may use the capacity conversion value C2 and a plurality of capacity conversion values determined in the capacity conversion value determination process one or more times before the capacity conversion value C2 determination process. In this case, the processing unit 80 may calculate the difference using the capacity conversion value C2 and the representative values of the plurality of capacity conversion values. For example, the representative value may be a statistical representative value, and may be various average values, median values, mode values, maximum values, minimum values, and the like.

  In the capacitance sensor according to the embodiment and the modified example, the processing unit 80 of the control unit 40 has the maximum capacitance conversion value of the sensor electrode 10 determined every second predetermined time T2 within the first predetermined time T1. When the fluctuation range is equal to or greater than the second predetermined capacity Cth1, it has been determined that the sensor electrode 10 is subjected to the action of electromagnetic waves, but the present invention is not limited to this. For example, the processing unit 80 extracts two capacity conversion values from a plurality of capacity conversion values Cnk (k = 1, 2,..., N) determined within the first predetermined time T1, These differences may be compared with the second predetermined capacity. Alternatively, the processing unit 80 may extract a plurality of pairs each constituted by two capacity conversion values from the plurality of capacity conversion values Cnk, and calculate a difference between the capacity conversion values in each pair. Further, the processing unit 80 may determine the presence or absence of the action of electromagnetic waves based on the number of times that the difference exceeds the threshold. In this case, the processing unit 80 may determine that the sensor electrode 10 is subjected to the action of electromagnetic waves when the number of times that the difference exceeds the threshold is equal to or greater than a predetermined number. Alternatively, the processing unit 80 may determine that the sensor electrode 10 is subjected to the action of electromagnetic waves when the representative value of the difference between the capacitance conversion values in each pair is equal to or greater than the threshold value corresponding to the second predetermined capacitance Cth1. Good. For example, the representative value may be a statistical representative value, and may be various average values, median values, mode values, maximum values, minimum values, and the like. Further, the processing unit 80 has determined the capacitance converted value of the sensor electrode 10 every second predetermined time T2 within the first predetermined time T1, but the period during which the capacitance converted value is established every second predetermined time T2. Is not limited to the first predetermined time T1, and may be any period.

  In the said embodiment and modification, although 2nd predetermined time T2 was a period shorter than 1st predetermined time T1, it is not limited to this, It is a period longer than 1st predetermined time T1, Also good.

  In the capacitance sensor according to the above-described embodiment and modification, the low-pass filter 20 includes the impedance element 21 that is a resistor and the reference capacitor 22, but is not limited thereto. For example, the low-pass filter 20 may be configured with an inductor and a reference capacitor 22 or may be configured with a resistor and an inductor.

  In the capacitance sensor according to the above-described embodiment and modification, the sensor electrode 10 includes the first electrode 11 and the second electrode 12, but is not limited thereto. The sensor electrode may have only one electrode electrically connected to the control unit 40, that is, only the first electrode 11. In this case, a capacitance is generated between the first electrode 11 and the object. And this electrostatic capacitance changes according to the distance between the 1st electrode 11 and a target object. Therefore, the capacitance sensor can detect the relative movement of the object by calculating the capacitance. Such a capacitance sensor may have a configuration in which the second electrode 12 is removed from the sensor electrode 10 in FIGS. 2 and 7, for example.

  The present disclosure can be applied to an apparatus that uses a detection result of relative movement such as approach, contact, and movement of an object with a potential of a human body or the like.

10 Sensor electrode 20 Low-pass filter 21 Impedance element (resistor)
31 1st switch 40 Control part 100,200 Capacitance sensor

Claims (8)

An electrode whose capacitance changes due to a change in distance from the object;
A controller electrically connected to the electrode;
A low pass filter connected between the electrode and the control unit;
A switch for switching on and off the low-pass filter by the control unit,
The controller is
Within the first predetermined period, the low-pass filter is turned on by the switch, and a first capacitance generated in the electrode is detected,
When the first capacitance changes by more than a first predetermined value, the switch turns off the low-pass filter, detects a second capacitance generated in the electrode within a second predetermined period, and the second A capacitance sensor that determines that an electromagnetic wave is applied to the electrode when a fluctuation range of the capacitance is equal to or greater than a second predetermined value. The capacitance sensor according to claim 1, wherein the first predetermined period is longer than the second predetermined period. The first predetermined period is a period corresponding to a moving speed of the object with respect to the electrode,
The capacitance sensor according to claim 2, wherein the second predetermined period is a period corresponding to a period of the electromagnetic wave. The controller is
Repeating the detection of the second capacitance within the second predetermined period;
The capacitance sensor according to any one of claims 1 to 3, wherein a fluctuation range between the second capacitances in the different second predetermined period is compared with the second predetermined value. The controller is
5. The capacitance sensor according to claim 4, wherein, within a predetermined period, a maximum value of a fluctuation range between the second capacitances in different second predetermined periods is compared with the second predetermined value. The controller is
Repeating the detection of the first capacitance within the first predetermined period;
The capacitance sensor according to any one of claims 1 to 5, wherein a change amount between the first capacitances in the different first predetermined period is compared with the first predetermined value. The capacitance sensor according to any one of claims 1 to 6, wherein the low-pass filter includes a resistor, and the switch is electrically connected to both ends of the resistor. The capacitance sensor according to claim 7, wherein the switch is directly connected to both ends of the resistor.

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