JP2004257976A - Method and device for detecting raindrop - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a malfunction at a low cost without providing a special circuit for temperature compensation. <P>SOLUTION: This raindrop detecting method shortens the time interval of updating past output values of a photoelectric conversion element 9 used for judging rain from B to A, if, when judged as fair weather, the rate of rising of environment temperature surrounding a light emitting element 8 and the photoelectric conversion element 9 is equal to or higher than a prescribed value. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a raindrop detection method suitable for use in a vehicle wiper automatic control device or a building window automatic opening / closing device and the like, and a device therefor.
[0002]
[Prior art]
2. Description of the Related Art Generally, a raindrop detecting device used in an automatic wiper control device for a vehicle or an automatic opening / closing device for a building window receives a light emitting element (for example, a light emitting diode LED) that irradiates light toward the window glass and receives reflected light from the window glass. A photoelectric conversion element (for example, a photodiode PD) for converting the signal into an electric signal, an output value of the photoelectric conversion element (strictly, an output value of a detection / amplification circuit connected to the photoelectric conversion element) and a threshold value for rain determination And an arithmetic processing circuit that determines whether the weather is fine or not, and controls the wiping operation mode of the wiper, the opening / closing operation of the window glass, and the like according to the state of raindrops attached to the window glass.
[0003]
However, since the light emission amount of the light emitting element and the output value of the photoelectric conversion element change with temperature, an erroneous determination is made based on the temperature characteristic of the photoelectric conversion element, and the wiper is operated even when it is sunny, or the open window glass is removed. A malfunction such as closing occurs.
[0004]
Therefore, conventionally, a raindrop detecting device has been known in which the gain and the reference voltage of the light receiving and amplifying unit are corrected in order to compensate the temperature characteristics of the output of the photoelectric conversion element (for example, see Patent Document 1).
[0005]
[Patent Document 1]
JP-A-11-326186
[Problems to be solved by the invention]
However, according to the conventional raindrop detecting device as described above, a light emission amount control circuit is required on the light emitting side, and a temperature correction circuit is required on the light receiving side, so that there is a problem that the cost increases.
[0007]
An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a raindrop detection method and a raindrop detection method capable of preventing malfunction at low cost without providing a special circuit for temperature compensation. And
[0008]
[Means for Solving the Problems]
The raindrop detection method according to claim 1, when the rate of increase in the environmental temperature surrounding the light emitting element and the photoelectric conversion element is equal to or greater than a predetermined value at the time of determining the fineness, the past output value of the photoelectric conversion element used for the rain determination is determined. It is characterized in that the update time interval is shortened.
[0009]
According to the raindrop detecting method of the first aspect, when the environmental temperature surrounding the light emitting element and the photoelectric conversion element changes rapidly, the past output value of the photoelectric conversion element used for rain determination is updated in a short period of time. Become like That is, when the environmental temperature changes rapidly, the output value after the characteristic has changed due to the temperature change is used for rain determination. For this reason, it is possible to prevent an erroneous determination that it is erroneously determined to be a rainfall despite a fine weather due to a change in the output value due to a temperature change. Such a reduction in the time interval for updating the past output values can be easily performed by software, so that a special circuit for temperature compensation as in the related art is not required, and malfunctions can be performed at low cost. Can be prevented. In addition, when the raindrop detection method is used for a vehicle wiper automatic control device, the update time interval of the past output value is shortened only when it is sunny, and when the rainfall occurs, the update of the past output value is performed at the previous update time interval. Is performed, the wiping operation of the wiper at the time of rainfall is performed in the same manner as before, and the wiping feeling does not deteriorate.
[0010]
The raindrop detection method according to claim 2 is characterized in that, at the time of clearness determination, when a rising rate of the environmental temperature surrounding the light emitting element and the photoelectric conversion element is equal to or more than a predetermined value, the threshold value for rain determination is changed by a predetermined amount. I do.
[0011]
According to the raindrop detecting method of the second aspect, when the environmental temperature surrounding the light emitting element and the photoelectric conversion element changes rapidly, the threshold value for rain determination changes by a predetermined amount. That is, when the environmental temperature changes rapidly, if the rain determination is performed using the threshold value before the change as it is, the output value changed due to the temperature change may erroneously determine that it is raining despite the fine weather. By using the threshold value changed only, it is possible to prevent an erroneous determination that a rainfall has occurred. Since the update of the threshold value for rain determination can be easily executed by software, a special circuit for temperature compensation as in the related art is not required, and malfunction is prevented at low cost. be able to. Also, when the raindrop detection method is used in the automatic wiper control device for a vehicle, the update of the threshold value for rain determination is performed only when it is sunny, and the conventional threshold value is used when it rains. The operation is performed as before, and the wiping feeling is not reduced.
[0012]
The raindrop detecting device according to claim 3, wherein the light emitting element irradiates light to the transparent plate, a photoelectric conversion element that receives light reflected from the transparent plate and outputs an electric signal according to a received light amount, and the photoelectric conversion element. Updating the past output value at a predetermined time interval, calculating an output change amount based on the updated past output value and the current output value, and comparing the output change amount with a predetermined threshold value. In a raindrop detection device comprising: an arithmetic processing circuit for determining whether it is fine or rain, comprises a temperature detection means for detecting an environmental temperature surrounding the light emitting element and the photoelectric conversion element, and the arithmetic processing circuit, when determining the fineness, When it is determined that the rise rate of the environmental temperature is equal to or more than the predetermined value, the update time interval of the past output value is shortened, and the past output value and the current output value updated at the update time interval after the shortening are reduced. Output change based on It calculates the amount, and judging the rain or shine by comparing the output variation with a predetermined threshold value.
[0013]
A raindrop detecting device according to a third aspect is a device for implementing the raindrop detecting method according to the first aspect, and similarly to the raindrop detecting method according to the first aspect, can be operated without providing a special circuit for temperature compensation. Malfunction can be prevented at a cost.
[0014]
The raindrop detecting device according to claim 4, wherein the light-emitting element irradiates light to the transparent plate, a photoelectric conversion element that receives reflected light from the transparent plate and outputs an electric signal according to a received light amount, and the photoelectric conversion element. A raindrop detection device comprising an arithmetic processing circuit that calculates an output change amount based on a past output value and a current output value of the current output value and compares the output change amount with a predetermined threshold to determine fine or rain. The light-emitting element and a temperature detection unit for detecting an environmental temperature surrounding the photoelectric conversion element, the arithmetic processing circuit, when determining the fine, when it is determined that the rise rate of the environmental temperature is a predetermined value or more, The threshold value is increased, and the threshold value after the increase is compared with an output change amount calculated based on the past output value and the current output value to determine fine weather.
[0015]
The raindrop detecting device according to claim 4 is a device for performing the raindrop detecting method according to claim 2, and is low in temperature without providing a special circuit for temperature compensation, similarly to the raindrop detecting method according to claim 2. Malfunction can be prevented at a cost.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0017]
FIG. 1 is a block diagram of an automatic wiper control device as a raindrop handling device incorporating a raindrop detection device according to an embodiment of the present invention, and FIG. 2 is a structural diagram of the raindrop detection device.
[0018]
In FIG. 1, reference numeral 1 denotes a window glass of an automobile as a transparent plate, for example, a front window, 2 denotes a wiper as an operation member for wiping raindrops attached to the front window 1, and 3 denotes an operation member driving device for driving the wiper 2 And a wiper driving device 6 that detects a raindrop attached to the front window 1 and transmits a wiper automatic control signal to the wiper driving device 3.
[0019]
Power is supplied to the automatic wiper control device from a battery 30 via an ignition switch 31 and is distributed to the CPU 12 in the raindrop detection device 6, the wiper motor 4 in the wiper drive device 3, and the like.
[0020]
The wiper driving device 3 includes a wiper motor 4 that drives the wiper 2, a wiper motor drive circuit 5 that supplies a drive current to the wiper motor 4, and a wiper switch 7 that is operated to determine an operation mode of the wiper 2. I have. The wiper switch 7 has four operation positions of stop (OFF), auto (AUTO), Lo and Hi. When the auto is selected, the wiper 2 is automatically controlled by the raindrop detector 6. Note that the wiper switch 7 only needs to have at least a switch for operating the raindrop detecting device 6, and does not need to have all the four operation positions.
[0021]
The raindrop detecting device 6 includes a light emitting element (light emitting diode LED) 8 that irradiates light (infrared light or visible light) to the front window 1 to optically detect raindrops on the front window 1, And a photoelectric conversion element (photodiode PD) 9 for receiving the reflected light and converting the reflected light into an electric signal. An LED drive circuit 13 is connected to the LED 8, and the LED drive circuit 13 pulse-drives the LED 8 according to a light emission timing control signal and a drive current control signal from the CPU 12. A detection / amplification circuit 14 is connected to the PD 9, and the detection / amplification circuit 14 detects and amplifies an output signal of the PD 9 and outputs the amplified signal to the CPU 12. It should be noted that a plurality of LEDs 8 and PDs 9 may be mounted, respectively, to expand the raindrop detection range.
[0022]
The CPU 12 calculates, stores and calculates the rate of decrease in the amount of received light with respect to the amount of emitted light based on the output value of the detection / amplification circuit 14 and the output value of the past detection / amplification circuit 14 stored through a predetermined procedure. It has a judgment function or the like for judging fine weather by comparing the reduced rate with a predetermined threshold value, and transmits a wiper control signal to the wiper motor drive circuit 5 based on the judgment result. Here, the output value of the past detection / amplification circuit 14 stored through a predetermined procedure is a state in which raindrops are not attached to the front window 1, that is, an output value at a sunny time. The attached value, that is, the output value at the time of rainfall is excluded. This output value is an output value that is constantly updated at regular intervals because the output value itself fluctuates due to stains and scratches on glass other than raindrops and deterioration of elements, in other words, an output value corrected for aging. is there. The CPU 12 includes a RAM 24 and a ROM 25 in which the above-described threshold values, output values, and the like, and predetermined processing procedures for executing automatic wiper control and the like are stored.
[0023]
The raindrop detecting device 6 includes a heater 20 for preventing dew condensation on the prism 23, a heater circuit 21 for supplying a drive current to the heater 20, and a temperature for detecting the temperature of the prism 23 (FIG. 2), if necessary. A prism temperature sensor 22 is provided as temperature detecting means. The CPU 12 transmits a heater control signal to the heater circuit 21 in accordance with the temperature signal from the prism temperature sensor 22, and controls energization of the heater 20. In some cases, the CPU 12 performs temperature correction of the rate of decrease in the amount of received light according to a temperature signal from the prism temperature sensor 22. The prism temperature sensor 22 may be omitted by using the temperature detection unit 10 instead of the prism temperature sensor 22 and estimating the prism temperature from the circuit temperature.
[0024]
Further, as shown in FIG. 2, the raindrop detecting device 6 includes a base 17 supporting the LED 8 and the PD 9, a circuit board 15 having an LED driving circuit 12 (FIG. 1) and a detection / amplifying circuit 14 (FIG. 1). Are provided. The LED 8, the PD 9, the base 17 and the circuit board 15 are fixedly arranged in a sensor case 16, and the sensor case 16 is fixed in the cover 11. The raindrop detecting device 6 is attached to the front window 1 by fixing the prism 23 to the vehicle interior side wall surface 1b of the front window 1 using a light-transmitting transparent adhesive. The mounting position of the raindrop detecting device 6 is within the operation range of the wiper 2, that is, the wiper wiping range in the front window 1 and does not obstruct the driver's front view. The positional relationship between the LED 8 and the PD 9 is set so that light emitted from the LED 8 to the front window 1 is obliquely opposed to the front window 1 so that the light is reflected by the front window 1 and enters the PD 9.
[0025]
The prism 23 has a function of refracting the light of the LED 8 so that the light from the LED 8 is surely incident on the PD 9 and of preventing disturbance light such as sunlight from the outside of the vehicle compartment or a street light from being incident on the PD 9. ing. The prism 23 has a plate-like portion 23a at the center, and lenses 23b are formed on both sides of the plate-like portion 23a so as to face the LEDs 8 and the PDs 9. When it is sunny, the light emitted from the LED 8 is totally reflected by the outside wall surface 1a of the front window 1 via the prism 23 and then totally reflected by the plate-like portion 23a as shown by the arrow in FIG. Next, the light is totally reflected again by the vehicle exterior wall surface 1a and then enters the PD 9. On the other hand, at the time of rainfall, the light emitted from the LED 8 is scattered by the raindrops R attached to the front window 1 and is not totally reflected on the outer wall surface 1a of the passenger compartment, so that the amount of light received by the PD 9 decreases. Therefore, it is possible to determine fine or rain based on this decrease in the amount of received light, and the CPU 12 determines fine or rain based on, for example, the current output value of the detection and amplification circuit 14 with respect to the output value of the detection and amplification circuit 14 in the past. Perform determination processing. Here, the decrease rate is
Reduction rate = (current output value-output value without raindrops attached) / (output value without raindrops attached)
Is represented by Note that a filter 19 for cutting visible light is provided between the prism 23 and the PD 9 as necessary.
[0026]
FIG. 3 shows a temperature characteristic diagram of the raindrop detecting device 6. As shown in FIG. 3, it can be seen that the output value of the raindrop detector 6, that is, the output value of the detection / amplification circuit 14, decreases as the temperature increases. Such a decrease in the output value is similar to a phenomenon in which the output value decreases due to the attachment of raindrops to the front window 1. Even if there is a case, it may be erroneously determined that it is during rainfall, and the wiper 2 may malfunction.
[0027]
In the CPU 12 as an arithmetic processing circuit, in order to prevent such a malfunction of the wiper 2 due to the temperature characteristics of the output value, the following change of the update time interval of the output value or change of the threshold value for rain determination is performed. .
[0028]
The flowchart illustrated in FIG. 4 illustrates a process related to changing the update time interval of the output value.
[0029]
In FIG. 4, the CPU 12 first sets the output update interval during a sunny time, that is, the update time interval between output values during a sunny time, to B (step S1), and then determines whether a raindrop is being detected, that is, whether it is a rainfall. Is determined (step S2). Here, the determination as to whether or not raindrop detection is being performed is made by determining whether or not the above-described output value decrease rate is equal to or greater than a predetermined threshold.
[0030]
When raindrops are not being detected, that is, when it is sunny, whether the temperature rise within a predetermined time is within a predetermined temperature range based on a temperature signal from the temperature detection means 10 or 22, for example, the temperature rise for 30 seconds is 2 ° C. or more It is determined whether or not (step S3). When the temperature rise for 30 seconds is less than 2 ° C., the output update interval at the time of sunny is set to B (step S4), and the process proceeds to the next processing (step S5). On the other hand, when the temperature rise for 30 seconds is 2 ° C. or more, the output update interval at the time of sunny is set to A shorter than B (step S6), and the process proceeds to the next process (step S5).
[0031]
On the other hand, when raindrops are being detected, that is, when it is raining, the output update during sunny is prohibited (step S7), and the process proceeds to the next process (step S5). Note that A and B are determined according to the characteristics of various elements used in the raindrop detector 6.
[0032]
The flowchart illustrated in FIG. 5 illustrates a process related to a change in the threshold value for rain determination.
[0033]
In FIG. 5, the CPU 12 first sets the output update interval at a sunny time, that is, the update time interval of the output value at a sunny time, to B (step S11), and then determines whether a raindrop is being detected, that is, whether it is a rainfall. Is determined (step S12). Here, the determination as to whether or not raindrop detection is being performed is made by determining whether or not the above-described output value decrease rate is equal to or greater than a predetermined threshold.
[0034]
When raindrops are not being detected, that is, when it is sunny, whether the temperature rise within a predetermined time is within a predetermined temperature range based on a temperature signal from the temperature detection means 10 or 22, for example, the temperature rise for 30 seconds is 2 ° C. or more It is determined whether or not (step S13). If the temperature rise for 30 seconds is less than 2 ° C., the rain determination threshold, that is, the threshold for rain determination is set to B (step S14), and the process proceeds to the next process (step S15). On the other hand, when the temperature rise for 30 seconds is 2 ° C. or more, the rain determination threshold is set to A which is larger than B (step S16), and the process proceeds to the next process (step S15).
[0035]
On the other hand, when raindrops are being detected, that is, when it is raining, the process proceeds to the next process (step S15). Note that A and B are determined according to the characteristics of various elements used in the raindrop detector 6.
[0036]
FIG. 6 is a structural diagram of a raindrop detecting device according to another embodiment.
[0037]
The raindrop detector 6 shown in FIG. 6 includes an LED 8, a PD 9, and a circuit board 15 having an LED drive circuit 13 (FIG. 1) and a detection / amplification circuit 14 (FIG. 1). The LED 8, the PD 9 and the circuit board 15 are fixedly arranged in the sensor case 16, and the sensor case 16 is fixed in the cover 11, is in close contact with the interior side wall surface 1 b of the front window 1 via the silicon sheet 41, and has a stopper. It is fixed by 42 and a fixing bracket 43. The mounting position of the raindrop detecting device 6 is within the operation range of the wiper 2, that is, the wiper wiping range in the front window 1 and does not obstruct the driver's front view. The positional relationship between the LED 8 and the PD 9 is set so that light emitted from the LED 8 to the front window 1 is obliquely opposed to the front window 1 so that the light is reflected by the front window 1 and enters the PD 9.
[0038]
The prism 23 has a shape different from that of the prism 23 shown in FIG. 2, but refracts the light of the LED 8 so that the light from the LED 8 is surely incident on the PD 9, and also controls the solar light and the street light from outside the vehicle compartment. It has a function of preventing disturbance light from entering the PD 9. When the light is fine, the light emitted from the LED 8 is totally reflected by the vehicle exterior wall surface 1a of the front window 1 via the prism 23 as shown by an arrow in FIG. On the other hand, in rainy weather, the light emitted from the LED 8 is scattered by the raindrops R attached to the front window 1 and is not totally reflected by the vehicle interior outer wall surface 1a, so that the amount of light received by the PD 9 is reduced.
[0039]
As described above, the raindrop detection method according to the first embodiment is used for rain determination when the rate of increase in the environmental temperature surrounding the light emitting element 8 and the photoelectric conversion element 9 is equal to or higher than a predetermined value at the time of clearing. The update time interval of the past output value of the photoelectric conversion element 9 is shortened.
[0040]
According to the raindrop detection method according to the first embodiment, when the environmental temperature surrounding the light emitting element 8 and the photoelectric conversion element 9 changes rapidly, the past output value of the photoelectric conversion element 9 used for rain determination is Will be updated in a short time. That is, when the environmental temperature changes rapidly, the output value after the characteristic has changed due to the temperature change is used for rain determination. For this reason, it is possible to prevent an erroneous determination that it is erroneously determined to be a rainfall despite a fine weather due to a change in the output value due to a temperature change. Such a reduction in the time interval for updating the past output values can be easily performed by software, so that a special circuit for temperature compensation as in the related art is not required, and malfunctions can be performed at low cost. Can be prevented. In addition, when the raindrop detection method is used for a vehicle wiper automatic control device, the update time interval of the past output value is shortened only when it is sunny, and when the rainfall occurs, the update of the past output value is performed at the previous update time interval. Is performed, the wiping operation of the wiper 2 at the time of rainfall is performed in the same manner as before, and the wiping feeling does not deteriorate.
[0041]
The raindrop detecting device for implementing the raindrop detecting method according to the first embodiment includes a light emitting element 8 for irradiating the transparent plate 1 with light, a light reflected from the transparent plate 1 and receiving light reflected from the transparent plate 1. A photoelectric conversion element 9 that outputs an updated electric signal, and updates a past output value of the photoelectric conversion element 9 at predetermined time intervals and calculates an output change amount based on the updated past output value and the current output value. In the raindrop detecting device 6 including an arithmetic processing circuit 12 for calculating and comparing the amount of change in output with a predetermined threshold value to determine fine weather, the raindrop detecting device 6 detects an environmental temperature surrounding the light emitting element 8 and the photoelectric conversion element 9. The arithmetic processing circuit 12 is provided with the temperature detecting means 10 or 22. When the fineness is judged, the arithmetic processing circuit 12 shortens the update time interval of the past output value when it judges that the rise rate of the environmental temperature is equal to or more than the predetermined value. At update time interval Calculating the output change amount based on the new and the past output value and the current output value, configured to determine the rain or shine by comparing the output variation with a predetermined threshold value.
[0042]
In addition, the raindrop detection method according to the second embodiment is configured such that, when the clearness is determined, when the rate of increase in the environmental temperature surrounding the light emitting element 8 and the photoelectric conversion element 9 is equal to or greater than a predetermined value, the threshold for rain determination is set to a predetermined amount I try to change it.
[0043]
According to the raindrop detecting method according to the second embodiment, when the environmental temperature surrounding the light emitting element 8 and the photoelectric conversion element 9 changes rapidly, the threshold value for rain determination changes by a predetermined amount. That is, when the environmental temperature changes rapidly, if the rain determination is performed using the threshold value before the change as it is, the output value changed due to the temperature change may erroneously determine that it is raining despite the fine weather. By using the threshold value changed only, it is possible to prevent an erroneous determination that a rainfall has occurred. Since the update of the threshold value for rain determination can be easily executed by software, a special circuit for temperature compensation as in the related art is not required, and malfunction is prevented at low cost. be able to. Further, when the raindrop detection method is used in the automatic wiper control device for a vehicle, the update of the threshold value for rain determination is performed only when it is sunny, and the conventional threshold value is used during rainfall. The wiping operation is performed in the same manner as before, and the wiping feeling does not deteriorate.
[0044]
The raindrop detecting device for implementing the raindrop detecting method according to claim 2 includes a light emitting element 8 for irradiating the transparent plate 1 with light, and an electric signal corresponding to the amount of light received by receiving reflected light from the transparent plate 1. And the output change amount is calculated based on the past output value and the current output value of the photoelectric conversion element 9, and the amount of output change is compared with a predetermined threshold to determine fine weather. In the raindrop detecting device 6 including the arithmetic processing circuit 12, a temperature detecting unit 10 or 22 for detecting an environmental temperature surrounding the light emitting element 8 and the photoelectric conversion element 9 is provided. When it is determined that the increase rate of the environmental temperature is equal to or more than the predetermined value, the threshold is increased, and the increased threshold is compared with the output change amount calculated based on the past output value and the current output value. Judgment of clear rain by So that constructed.
[0045]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the raindrop detection method and apparatus of this invention, a malfunction can be prevented at low cost, without providing a special circuit for temperature compensation.
[Brief description of the drawings]
FIG. 1 is a block diagram of an automatic wiper control device as a raindrop handling device incorporating a raindrop detection device according to an embodiment of the present invention.
FIG. 2 is a structural diagram of a raindrop detecting device.
FIG. 3 is a temperature characteristic diagram of an output value.
FIG. 4 is a flowchart of processing relating to a change in an output value update time interval by a CPU.
FIG. 5 is a flowchart of a process for changing a threshold value for determining a raindrop state by a CPU.
FIG. 6 is a structural diagram of a raindrop detecting device according to another embodiment.
[Explanation of symbols]
1 Window glass (transparent plate material)
Reference Signs List 6 raindrop detecting device 8 light emitting element 9 photoelectric conversion element 12 arithmetic processing circuit 10, 22 temperature detecting means

Claims (4)

At the time of fineness judgment, when the rise rate of the environmental temperature surrounding the light emitting element and the photoelectric conversion element is a predetermined value or more, the update time interval of the past output value of the photoelectric conversion element used for rain determination is shortened. Raindrop detection method. A raindrop detection method comprising: changing a threshold for rain determination by a predetermined amount when a rise rate of an environmental temperature surrounding a light emitting element and a photoelectric conversion element is equal to or more than a predetermined value at the time of determining fineness. A light-emitting element that irradiates light to the transparent plate, a photoelectric conversion element that receives reflected light from the transparent plate and outputs an electric signal according to the amount of light received, and outputs a past output value of the photoelectric conversion element at a predetermined time interval. And an arithmetic processing circuit that calculates the output change amount based on the past output value after the update and the current output value and compares the output change amount with a predetermined threshold to determine fine or rain. In the raindrop detection device provided,
A temperature detecting unit for detecting an environmental temperature surrounding the light emitting element and the photoelectric conversion element,
The arithmetic processing circuit shortens the update time interval of the past output value when it is determined that the rise rate of the environmental temperature is equal to or greater than a predetermined value at the time of the fineness determination, and updates the update time interval with the update time interval after the shortening. A raindrop detecting device which calculates an output change amount based on a past output value and a current output value, and judges fine rain by comparing the output change amount with a predetermined threshold value. A light-emitting element that irradiates light to the transparent plate, a photoelectric conversion element that receives reflected light from the transparent plate and outputs an electric signal according to a received light amount, a past output value and a current output value of the photoelectric conversion element And a calculation processing circuit that determines fine weather by comparing the output change amount with a predetermined threshold value.
A temperature detecting unit for detecting an environmental temperature surrounding the light emitting element and the photoelectric conversion element,
The arithmetic processing circuit increases the threshold value when it is determined that the rise rate of the environmental temperature is equal to or more than a predetermined value at the time of the fineness determination, and increases the threshold value, the past output value, and the current output value. A raindrop detection device characterized in that a clear rain is determined by comparing an output change amount calculated on the basis of the output change amount.

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