WO2019182033A1

WO2019182033A1 - Drowsiness detection device

Info

Publication number: WO2019182033A1
Application number: PCT/JP2019/011790
Authority: WO
Inventors: 佐藤　寧
Original assignee: 国立大学法人九州工業大学
Priority date: 2018-03-22
Filing date: 2019-03-20
Publication date: 2019-09-26
Also published as: JPWO2019182033A1

Abstract

Provided is a drowsiness detection device that has high detection accuracy, is easy to install and operate, and can be implemented at low cost. The drowsiness detection device detects that a driver has become drowsy from a change in the center of gravity balance of the driver's trunk. After values from pressure sensors disposed on the right and left of a driver's seat are subjected to differential amplification, the values are converted into absolute values and then compared with a first threshold value to detect an unbalanced state of the driver's trunk, i.e., a rowing-motion state. Meanwhile, HPF is applied to data obtained by the differential amplification to detect an operation in which the driver has stepped on the brake pedal in a rushed way.

Description

Dozing detection device

[Technical Field] The present invention relates to a snoozing detection device that detects the snoozing of a driver of a passenger car.

A driver's doze while driving a passenger car contributes to the occurrence of a traffic accident. In particular, for drivers engaged in the transportation industry, the accumulation of fatigue caused by long working hours often induces a doze and is recognized as a social problem.
Devices that detect a driver's sleep at an early stage and issue a warning to the driver to prevent the driver's sleep are being developed in various forms. For this reason, a variety of techniques for detecting the driver's drowsiness have been considered.

Patent Document 1 discloses a pulse sensor which is the inventor's invention.
Patent Document 2 discloses a dozing prevention apparatus and method for detecting a driver's dozing by detecting eye movements.

Table 2015/56740 JP 2013-85576 A

The dozing alarm device detects the driver's falling asleep and sounds an alarm. In order to detect the driver's drowsiness, the driver's biological information is measured, a predetermined calculation process is performed on the measured biological information, and the result of the calculation process indicates whether the driver is asleep. Judge whether or not. Various snoozing alarm devices and snoozing detection devices have been developed, but as described above, the basic idea of information processing is common.
Japanese Patent Application Laid-Open No. 2004-151620 discloses technical contents related to a sensor for detecting a heartbeat of a driver. The technique described in Patent Literature 1 performs predetermined arithmetic processing such as Fourier transform on the detected driver's heartbeat information to determine whether or not the driver is asleep.
Patent Document 2 discloses the technical content of detecting the driver's eye movement and detecting the driver's drowsiness.
In addition to the above, various methods have been developed depending on how the driver's biometric information is measured and what calculation processing is performed.

In order to popularize the dozing alarm device or the dozing detection device, first, high detection accuracy is required.
Secondly, it is required that the apparatus is easily installed. It is ideal that the end user can purchase it at a mass retailer or the like and install it easily in the passenger car rather than one that can only be installed during the manufacturing process of the passenger car.
Thirdly, it is required that the operation of the apparatus is easy. For example, a sensor that is in contact with the skin of the driver is not preferable from the viewpoint of ease of operation. It is desirable that the driver is not in contact with the driver or that the driver does not need to be aware of the operation of the device.
Fourth, the device is required to be inexpensive. In order to realize a low price using a microcomputer, it is preferable that the amount of calculation is small. When the amount of calculation is large, the calculation processing capability of the microcomputer necessary for realizing the desired function increases, leading to an increase in the cost of the entire apparatus.

The inventor succeeded in satisfying the first to third conditions in Patent Document 1. However, under the condition of the fourth device cost, the cost increases in the final data processing part.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a dozing detection device that has high detection accuracy, is easy to install and operate, and can be realized at low cost.

In order to solve the above-described problem, the dozing detection device of the present invention includes a first pressure sensor disposed on the left side of the seat of the driver's seat and a second pressure sensor disposed on the right side of the seat. A first differential amplifier that obtains a differential output; an absolute value processing unit that outputs an absolute value of an output value of the first differential amplifier; and an output value of the absolute value processing unit that is compared with a first threshold value. And a first comparator that outputs a logical value for detecting the inclination of the trunk of the driver sitting on the seat. Further, a high-pass filter that outputs a differential value of the output value of the absolute value processing unit, a zero-cross detection unit that detects a zero-cross of the output value of the high-pass filter, and a predetermined value while the logical value of the first comparator indicates logic true A timer that counts the clock and is reset by the logic value of the zero-cross detection unit, and compares the count value of the timer with the second threshold value and outputs a logic value that detects whether or not the driver is asleep. Two comparators.

According to the present invention, it is possible to provide a dozing detection device that has high detection accuracy, is easy to install and operate, and can be realized at low cost.
Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

1 is an external view of a dozing detection device according to an embodiment of the present invention. It is a block diagram which shows the hardware constitutions of a dozing detection apparatus. It is a block diagram which shows the software function of a dozing detection apparatus. 5 is a time chart of each part in the dozing detection device in a state in which the driver depresses the brake pedal in a normal state and in a state in which a driver in a dozing state suddenly notices and stepped on the brake pedal. It is the schematic and pressure detection circuit of the pressure sensor which concern on a 1st example, and the schematic and pressure detection circuit of the pressure sensor which concerns on a 2nd example.

[Dozing detection device: Overview]
The inventor has realized a non-contact pulse sensor using radio waves in Patent Document 1. However, the final doze detection using the pulse data requires a large-capacity memory and an enormous calculation process such as discrete Fourier transform. In the discrete Fourier transform, a low-cost one-chip microcomputer has a heavy calculation load and a RAM capacity. In addition, since the heart rate is a low frequency of about several Hz, a data sample of about several seconds to several tens of seconds is required to execute arithmetic processing such as discrete Fourier transform. This lacks the real-time nature of dozing detection, which requires quick detection.

Recently, the inventor succeeded in detecting the driver's drowsiness by an approach completely different from the technique disclosed in Patent Document 1. It is a technology that measures the movement of the driver's center of gravity by detecting a characteristic movement called “boating” that occurs in the trunk (torso) movement of the driver due to falling asleep instead of a pulse. . That is, the driver's drowsiness is detected from the movement of the driver's center of gravity.

[Dozing detection device 101: schematic diagram and external view]
FIG. 1A is a schematic view of a driver's seat and driver of a passenger car as viewed from the side.
FIG. 1B is a diagram illustrating a state in which the trunk swings to the left and right when the driver falls asleep.
FIG. 1C is a schematic view of a driver seat and a pressure sensor embedded in the driver seat.
FIG. 1D is a diagram illustrating the positional relationship between the driver and the pressure sensor and the dozing detection device 101 connected to the pressure sensor.

As shown in FIG. 1A, the driver 102 who has accumulated fatigue begins to fall asleep while driving a passenger car (not shown). Then, as shown in FIG. 1B, a so-called “boat rowing” operation in which the upper body slowly swings left and right is performed unconsciously. Then, the right and left balance of the pressure applied to the seat chair 103a of the driver's seat 103 from the hips and thighs of the driver 102 changes.

As shown in FIG. 1C and FIG. 1D, the pressure sensors are provided at four locations of the seat chair 103 a of the driver's seat 103. The first pressure sensor 104 detects the pressure applied from the right thigh of the driver 102. Similarly, the second pressure sensor 105 is applied from the left thigh of the driver 102, the third pressure sensor 106 is applied from the starboard part of the driver 102, and the fourth pressure sensor 107 is applied from the port part of the driver 102. Detect each.
As shown in FIG. 1D, the dozing detection device 101 is connected to a first pressure sensor 104, a second pressure sensor 105, a third pressure sensor 106, and a fourth pressure sensor 107. The dozing detection device 101 generates an analog voltage signal corresponding to the pressure applied to each connected pressure sensor, converts the analog voltage signal into digital data, performs arithmetic processing described later, and performs a driver 102 operation. It is determined whether or not is in a doze state.

[Dozing detection device 101: hardware configuration]
FIG. 2 is a block diagram illustrating a hardware configuration of the dozing detection apparatus 101.
The dozing detection device 101, which is a computer such as a one-board microcomputer, is connected to the bus 201 and outputs a logical signal of the determination result to the CPU 202, ROM 203, RAM 204, and any external device (“serial” in FIG. 2). "I / F", hereinafter abbreviated as "serial I / F") 205. The ROM 203 stores a program for operating the microcomputer as the dozing detection device 101.
Further, a first pressure sensor 104, a second pressure sensor 105, a third pressure sensor 106, and a fourth pressure sensor 107 are connected to the bus 201 through an A / D converter 206 and a multiplexer 207. That is, analog signals output from the first pressure sensor 104, the second pressure sensor 105, the third pressure sensor 106, and the fourth pressure sensor 107 are selected by the multiplexer 207 and then converted into digital data by the A / D converter 206. Converted.

The multiplexer 207 switches in synchronization with the sampling clock of the A / D converter 206. In the case of the dozing detection device 101 according to the embodiment of the present invention, the frequency of the sampling clock of the A / D converter 206 is 280 Hz. Therefore, the first pressure sensor 104, the second pressure sensor 105, the third pressure sensor 106, and The sampling clock of the fourth pressure sensor 107 is ¼, 70 Hz.
The dozing detection device 101 detects the trunk movement of the driver 102 with the first pressure sensor 104, the second pressure sensor 105, the third pressure sensor 106, and the fourth pressure sensor 107. Since the rowing operation is an extremely low frequency of less than 1 Hz and the sudden braking is a frequency of about several Hz, the sampling clock is sufficient at a low frequency. The fact that the sampling clock has a low frequency means that the required specifications can be satisfied even if the microcomputer has a low processing capacity per unit time.

[Dozing detection device 101: software function]
FIG. 3 is a block diagram illustrating software functions of the dozing detection apparatus 101. In the block diagram shown in FIG. 3, circuit symbols described by analog operational amplifiers such as differential amplifiers are software components that receive digital data input and realize arithmetic processing having functions equivalent to those of the analog operational amplifier.
Analog signals output from the first pressure sensor 104, the second pressure sensor 105, the third pressure sensor 106, and the fourth pressure sensor 107 are converted into digital data by the A / D converter 206. In FIG. 3, the multiplexer 207 is omitted to simplify the description.

The first adder 301 adds the digital data of the first pressure sensor 104 and the digital data of the third pressure sensor 106. That is, the first adder 301 adds the pressure data of the right thigh of the driver 102 and the pressure data of the starboard region, whereby the pressure data of the right half of the driver 102 is obtained from the first adder 301.
The digital data of the second pressure sensor 105 and the digital data of the fourth pressure sensor 107 are added by the second adder 302. That is, the pressure data of the left thigh of the driver 102 and the pressure data of the left buttock of the driver 102 are added by the second adder 302, whereby the pressure data of the left body of the driver 102 is obtained from the second adder 302.

The output data of the first adder 301 and the output data of the second adder 302 are differentially amplified by the first differential amplifier 303. The output data from the first adder 301 and the output data from the second adder 302 are added by the third adder 304.
The output gain of the output data of the first differential amplifier 303 is adjusted by an AGC (Auto Gain Control) 305. Since the AGC 305 is adjusted by the output data of the third adder 304, the AGC 305 excludes the dependent element due to the weight of the driver 102 from the output data of the first differential amplifier 303.
In the output data of the AGC 305, a negative value is converted into a positive value by the absolute value processing unit 306. By this absolute value processing unit 306, the left-right unbalanced component of the load applied to the pressure sensor, which is caused by the angle at which the trunk is tilted, appears as a positive value regardless of whether the trunk of the driver 102 is tilted to the left or right. .

The data output from the absolute value processing unit 306 is input to the plus side input of the first comparator 307. The first comparator 307 compares the first threshold value 308 connected to the minus side input with the value of the plus side input, and if the data output from the absolute value processing unit 306 is equal to or greater than the first threshold value 308, the logic The true of is output.
Further, the data output from the absolute value processing unit 306 is input to the non-inverting input of the second differential amplifier 309. To the inverting input of the second differential amplifier 309, the data output from the absolute value processing unit 306 is input through the low-pass filter (indicated as “LPF” in the figure, hereinafter abbreviated as “LPF”) 310. The second differential amplifier 309 subtracts the data that has passed through the LPF 310 to the inverting input from the data that has not passed through the LPF 310 that is input to the non-inverting input. It functions as a high-pass filter (hereinafter abbreviated as “HPF”) 325 that outputs a differential component.

The output data of the second differential amplifier 309 is input to the zero cross detection unit 311. The zero cross detection unit 311 is equivalent to a comparator having hysteresis, and binarizes input data. Therefore, the output of the zero-cross detection unit 311 is a logical true or false binary value.
The output logical value of the first comparator 307 is input to the D terminal of a D flip-flop (hereinafter abbreviated as “D-FF”) 313 via a NOT gate 312, and is set as it is in the set terminal of the D-FF 313 (in FIG. 3). It is also input to “S” (hereinafter abbreviated as “S terminal”). The output logical value of the zero cross detector 311 is input to the clock terminal of the D-FF 313. Although not shown, the reset terminal (R terminal) of the D-FF 313 is always held in a logic false state.

The Q terminal of the D-FF 313 is connected to one input terminal of the AND gate 314. The other input terminal of the AND gate 314 is connected to the output terminal of the first comparator 307. The output terminal of the AND gate 314 is connected to the reset terminal of the timer 315. The output data of the timer 315 is input to the latch 316.
The control input terminal of the latch 316 is connected to the output terminal of the zero cross detector 311. The latch 316 holds the current value when a pulse is generated from the zero cross detector 311. The output data of the latch 316 is supplied to the non-inverting input of the second comparator 317. The second comparator 317 compares the second threshold value 318 connected to the inverting input with the value of the non-inverting input, and when the data output from the latch 316 is equal to or higher than the second threshold value 318, the logic is true. An alarm indicating that there is a high possibility that the driver 102 is in a dozing state is output.

[Dozing detection device 101: operation]
FIG. 4A is a time chart of each part in the dozing detection device 101 when the driver 102 is in a normal state and the brake pedal is depressed.
The output data S401 (probe point P321 in FIG. 3) of the absolute value processing unit 306 shows a peak at the moment when the driver 102 depresses the brake pedal, and thereafter maintains a state in which a little value has passed.
As the differential component S402 (probe point P322 in FIG. 3) of the output data S401 of the absolute value processing unit 306, a component having a polarity opposite to the direction in which the brake pedal is stepped on instantaneously is output, and then the polarity is inverted to zero. Return.

The output logical value S403 of the AND gate 314 (probe point P323 in FIG. 3) input to the reset terminal of the timer 315 is logically detected by the D-FF 313 from the up edge of the first comparator 307 by the up edge of the differential component S402. It will be logical true until it shows true. Therefore, the timer 315 waits for a time T405 until the force applied to the brake pedal slightly decreases while the AND gate 314 indicates the logic true, that is, a little after the driver 102 starts to step on the brake pedal. measure.
Since the measurement time interval of the timer 315 is short, the output data L406 of the timer 315 is extremely small.

FIG. 4B is a time chart of each part in the dozing detection apparatus 101 in a state where the driver 102 in the dozing state notices and suddenly steps on the brake pedal.
As for the driver 102, the trunk gradually begins to tilt as the patient falls asleep. Then, the value of the output data S411 (P321) of the absolute value processing unit 306 gradually increases according to the angle at which the trunk of the driver 102 tilts. When the value is greater than or equal to the first threshold, the first comparator 307 indicates logic true. That is, the first comparator 307 detects that the trunk of the driver 102 has been tilted due to the driver 102 falling into a doze state. When the driver 102 suddenly notices that he / she is snoozing and steps on the brake pedal, the output data S411 of the absolute value processing unit 306 changes abruptly at the moment the driver 102 steps on the brake pedal. After that, the value returns to almost zero.

In the differential component S412 (P322) of the output data S411 of the absolute value processing unit 306, only a state in which the driver 102 in a dozing state notices and suddenly steps on the brake pedal appears. In other words, the slow change in the output data S411 of the absolute value processing unit 306, which is detected by the first comparator 307 and the trunk of the driver 102 slowly tilts, does not appear. In the differential component S412 of the output data S411, a component having a polarity opposite to the direction in which the brake pedal is depressed instantaneously is output, and then the polarity is inverted to return to zero.

The output logic value S413 (P323) of the AND gate 314 input to the reset terminal of the timer 315 is logical from the up edge of the first comparator 307 until the D-FF 313 indicates logic true by the up edge of the differential component. Become true. Therefore, the timer 315 detects the force applied to the brake pedal while the AND gate 314 indicates the logic true, that is, from the time when the trunk of the driver 102 starts to tilt, and the driver 102 suddenly steps on the brake pedal. The time T415 until the time when it slightly decreases is measured. Then, the measurement time of the timer 315 is significantly longer than that in the normal state. Therefore, the output data L416 of the timer 315 shows a large value.

[Example of pressure sensor]
The dozing detection apparatus 101 according to the embodiment of the present invention observes a change in a voltage signal obtained from a pressure sensor through arithmetic processing. For this reason, the pressure sensor used for the dozing detection apparatus 101 according to the embodiment of the present invention does not require strict linearity. Even if the voltage signal output according to the magnitude of the pressure includes some errors, it is only necessary to detect the voltage fluctuation. Therefore, a pressure sensor having a simple configuration can be used instead of an expensive pressure sensor in which the linearity of the output signal is guaranteed.

FIG. 5A is a schematic diagram of a pressure sensor 501 according to a first example. The pressure sensor 501 has a configuration in which electrodes are attached to both surfaces of a conductive rubber sheet 502. When pressure is applied to the sheet-like pressure sensor 501, the resistance of the pressure sensor 501 decreases because the density of the conductive rubber forming the sheet 502 increases.
FIG. 5B is a pressure detection circuit using the pressure sensor 501 according to the first example. By applying a constant voltage to the resistance type pressure sensor 501 via the resistor R503, an analog voltage signal corresponding to the pressure can be obtained. By inputting this analog voltage signal to the A / D converter 206, it is possible to obtain digital data whose value fluctuates in response to the magnitude of pressure.

The pressure sensor 501 according to the first example shown in FIGS. 5A and 5B can easily acquire an analog voltage signal corresponding to pressure with a very simple circuit configuration. However, in the pressure detection circuit of FIG. 5B, current always flows through the resistor. That is, a through current is always generated. For this reason, it cannot be said that it is not very suitable for a battery drive circuit. An example of an electrostatic pressure sensor that does not have room for through current will be described below.

FIG. 5C is a schematic diagram of a pressure sensor 511 according to the second example. The pressure sensor 511 shown in FIG. 5C has a configuration in which electrodes are attached to both surfaces of a dielectric rubber sheet 512 as an insulator. When pressure is applied to the sheet-like pressure sensor 511, the distance between the electrodes is shortened, so that the capacitance of the pressure sensor 511 increases.
FIG. 5D is a pressure detection circuit using the pressure sensor 511 according to the second example.

The signal source 513 generates a rectangular wave signal having a frequency higher than the audible frequency band, for example, 30 kHz or higher. The rectangular wave signal is applied to the gate of the CMOS inverter 514. Then, the output terminal of the CMOS inverter 514 causes the forward current (source) and the reverse current (sink) to flow through the subsequent resistor R515 with logic inverted with respect to the rectangular wave signal. That is, the CMOS inverter 514 operates as a changeover switch that alternately connects the power supply node and the ground node to the resistor R515. Due to the presence of the CMOS inverter 514, no through current is generated in the pressure detection circuit of FIG. 5D.

A variable capacitor C516 constituting the pressure sensor 511 is connected to the other end of the resistor R515. Therefore, the resistor R515 and the variable capacitor C516 constitute a time constant. This time constant varies depending on the capacitance of the variable capacitor C516. That is, if the period of the rectangular wave signal of the signal source 513 is shorter than the time required for charging and discharging the variable capacitor C516, the voltage at the peak of the variable capacitor C516 varies depending on the capacitance of the variable capacitor C516. To do. When the capacitance of the variable capacitor C516 is small, the peak voltage is high. Conversely, when the capacitance of the variable capacitor C516 is large, the peak voltage is low.

The anode of a diode D517 is connected to the connection point between the variable capacitor C516 and the resistor R515. The cathode of the diode D517 is connected to a capacitor C518 having a larger capacitance than the variable capacitor C516. A resistor R519 is connected in parallel to the capacitor C518, and the capacitor C518 and the resistor R519 have a time constant of several tens to several thousand times the period of the rectangular wave signal. As the diode D517, a Schottky barrier diode with a small forward voltage drop and high-speed switching is suitable.

When the voltage of the capacitor C518 is lower than the voltage obtained by subtracting the forward voltage drop of the diode D517 from the voltage of the variable capacitor C516, the capacitor C518 is charged from the variable capacitor C516 through the diode D517. At this time, the discharge of the capacitor C518 to the variable capacitor C516 is blocked by the diode D517, and is discharged only by the resistor R519. Therefore, the diode D517, the capacitor C518, and the resistor R519 constitute a simple peak hold circuit. If the time constant of the capacitor C518 and the resistor R519 is sufficiently larger than the time constant of the variable capacitor C516 and the resistor R515, the voltage fluctuation of the capacitor C518 can be reduced. Therefore, by inputting the voltage of the capacitor C518 to the A / D converter 206, digital data whose value fluctuates in accordance with the pressure can be obtained.

In each embodiment of the present invention, the dozing detection device 101 is disclosed.
The dozing detection device 101 detects that the driver 102 has fallen asleep from the change in the center of gravity balance of the trunk of the driver 102. The center of gravity balance of the trunk of the driver 102 is detected by a pressure sensor. After differentially amplifying the values of the pressure sensors provided on the left and right sides of the driver's seat 103, the values are converted into absolute values and compared with a predetermined first threshold value 308, thereby unbalanced the trunk of the driver 102 That is, the rowing state is detected. On the other hand, HPF is applied to the differentially amplified data, and the operation of hitting the brake is detected. Under normal braking conditions, the counter value remains small because there is no long-term rowing condition. In the brake operation that is noticed from dozing and stepped on in a hurry, there is a long-time rowing state, so the value of the counter becomes large, and the dozing state can be detected.

It is necessary to handle an extremely low frequency signal of less than 1 Hz for detecting a dozing state. An analog circuit requires a large-capacitance capacitor, but by converting it to digital data, it is possible to complete it all by microcomputer processing. Further, since the frequency of the signal to be handled is an extremely low frequency, the sampling clock may be low. Furthermore, the dozing detection apparatus 101 according to the embodiment of the present invention does not perform enormous calculations such as Fourier transform. Therefore, even an 8-bit one-chip microcomputer having a smaller arithmetic processing capability than a personal computer can be used sufficiently.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, Unless it deviates from the summary of this invention described in the claim, another modification example and application example Including.

DESCRIPTION OF SYMBOLS 101 ... Dozing detection apparatus, 102 ... Driver, 103 ... Driver's seat, 103a ... Seat chair, 104 ... First pressure sensor, 105 ... Second pressure sensor, 106 ... Third pressure sensor, 107 ... Fourth pressure sensor , 201 ... bus, 202 ... CPU, 203 ... ROM, 204 ... RAM, 205 ... serial interface, 206 ... A / D converter, 207 ... multiplexer, 301 ... first adder, 302 ... second adder, 303 ... First differential amplifier 304 ... third adder 305 ... AGC 306 ... absolute value processing unit 307 ... first comparator 308 ... first threshold value 309 ... second differential amplifier 310 ... LPF 311 ... Zero cross detector, 312 ... NOT gate, 313 ... D? FF, 314 ... AND gate, 315 ... Timer, 316 ... Latch, 317 ... Second controller Parator, 318 ... second threshold, 325 ... HPF, 501, 511 ... pressure sensor, 502, 512 ... sheet, 513 ... signal source, 514 ... CMOS inverter, C516 ... variable capacitor, C518 ... capacitor, D517 ... diode, R503 , R515, R519 ... resistance

Claims

A first differential amplifier for obtaining a differential output between a first pressure sensor disposed on a left side of a seat chair of a driver's seat of a vehicle and a second pressure sensor disposed on a right side of the seat;
An absolute value processing unit for outputting an absolute value of an output value of the first differential amplifier;
A first comparator that compares the output value of the absolute value processing unit with a first threshold value and outputs a logical value for detecting the inclination of the trunk of the driver seated on the driver's seat;
A high-pass filter that outputs a differential value of the output value of the absolute value processing unit;
A zero-cross detector that detects a zero-cross of the output value of the high-pass filter;
A timer that counts a predetermined clock while the logic value of the first comparator indicates logic true, and is reset by the logic value of the zero-cross detector;
A dozing detection apparatus comprising: a second comparator that compares a count value of the timer with a second threshold value and outputs a logical value for detecting whether or not the driver is dozing.
Furthermore,
The dozing detection apparatus according to claim 1, further comprising a latch interposed between the timer and the second comparator and latching an input value according to an output logical value of the zero-cross detection unit.
The first pressure sensor and the second pressure sensor are
A variable capacitance capacitor whose capacitance fluctuates in response to the load and whose one terminal is connected to the ground node;
A first resistor having one terminal connected to the other terminal of the variable capacitor and forming a first time constant;
A changeover switch that alternately switches between a power supply node and a ground node with respect to the other terminal of the first resistor;
A diode having an anode connected to a connection point between the variable capacitor and the first resistor;
A capacitor connected between the cathode of the diode and a ground node and having a capacitance greater than the variable capacitor;
The dozing detection device according to claim 2, further comprising: a second resistor connected in parallel with the capacitor and forming a second time constant larger than the first time constant.
The dozing detection apparatus according to claim 2, wherein the first pressure sensor and the second pressure sensor are variable resistors having a resistance film whose resistance value varies in response to a load.