TECHNICAL FIELD
[0001] The present invention lies within the field of traffic monitoring, in particular
within the field of vehicle sensing devices.
BACKGROUND OF THE INVENTION
[0002] Road traffic monitoring is an important tool for traffic management and for infrastructure
development. Information regarding e.g. type, frequency, speed, etc. for vehicles
is traditionally produced by people who sit by the road and manually collect the information.
However, devices for collecting this information have started to replace these people,
making the collection less labor intensive, cheaper and most importantly improving
safety.
[0003] Traditionally, devices such as radar devices, inductive loops, and cameras are used
for detecting vehicles. Another more recently introduced type of vehicle detecting
device utilizes sensors such as magnetometers and accelerometers for detecting vehicles.
These devices are in general driven by batteries.
[0004] A problem with these battery driven devices is that the batteries need to be replaced
from time to time, which requires both systems for indicating when the battery needs
to be replaced, and requires further the actual service of replacing the batteries.
Moreover, the sensors in the devices are often very power-consuming and thus the batteries
need to be replaced often.
[0005] A solution to this problem is to include a solar cell in the device. Thereby, the
device may be powered by the solar cell when there is sufficient light. Thus, battery
life is extended.
[0006] Another solution is to utilize duty cycling in the device. By duty cycling, the device,
or parts of the device, goes into a sleep mode frequently which utilizes less power.
Thus, battery life is extended.
[0007] However, there is still a need for improvement of these devices, in particular concerning
their power consumption.
SUMMARY OF THE INVENTION
[0008] An object of the present invention is to alleviate the above mentioned drawbacks
and problems. A further object is to provide a method and a sensor device with lowered
power consumption in comparison to known techniques.
[0009] According to a first aspect of the invention, this and other objects are achieved
by a method for operating a vehicle sensor device between a sleep mode and an active
mode, the method comprising: generating, when the vehicle sensor device is in the
sleep mode and when a photoelectric cell receives light, an input signal by the photoelectric
cell; and activating, provided that the input signal lies within a predetermined interval
and thereby assuming that at least a part of the received light is provided by a light
source on a vehicle, a sensor in the vehicle sensor device by a controller, thereby
setting the vehicle sensor device in the active mode.
[0010] The invention includes, and is based on, the realization that a photoelectric cell
can be utilized for detecting a vehicle. This is a novel concept which solves many
of the problems mentioned above. The photoelectric cell does not consume any power
for receiving light, thus proving a large reduction in power-consumption relative
to conventional vehicle sensors such as magnetometers and accelerometers.
[0011] The sensor is activated by the controller. The controller is preferably a micro controller,
but could be other types of controllers as well, such as a field-programmable gate
array (FPGA), a digital signal processor (DSP) or any other suitable controller.
[0012] During night, or during cloudy days, daylight is weak and not sufficient to power
the sensor device by means of the photoelectric cell. However, the photoelectric cell
still generates electric signals when receiving light. When the photoelectric cell
receives light from the light source, such as a headlight on the vehicle, the photoelectric
cell generates an input signal. If the light originates only from the vehicles headlight,
the input signal is of a voltage much smaller than from e.g. daylight on a sunny day.
Even if the input signal is not sufficient to power to sensor device, it may still
utilized for activating the sensor in the vehicle sensor device, thereby setting the
vehicle sensor device in the active mode. It is assumed that the light originates
from a light source such as a headlight of a vehicle, if the input signal lies within
the predetermined interval. Thus, the vehicle sensor device may be activated when
a vehicle is driving nearby the sensor.
[0013] By that the input signal lies within a predetermined interval is meant that the strength
of the input signal, such as the voltage value of the input signal, lies within a
predetermined strength interval, such as a voltage interval.
[0014] Preceding the step of activating, the input signal may be amplified. The input signal
may be amplified using an operational amplifier. Such an amplifier is cheap and has
low power consumption.
[0015] By the amplification, the amplified signal may be measured on by a controller having
a conventional A/D converter. Such an A/D converter has typical a resolution of 10-16
bits. Preferably, the input signal is amplified with an amplification factor in a
range of 100-10 000, i.e. the input signal is amplified by 100-10 000 times. By using
an amplifier and a controller having a conventional A/D converter, the method may
be achieved in a cheap and simple manner.
[0016] Alternatively, the input signal may, without being amplified, be measured on by a
controller with a high resolution A/D converter. Such an A/D converter may have a
high resolution of 18-24 bits.
[0017] The vehicle sensor device may switch between the sleep mode and the active mode at
least during periods in which there is not sufficient daylight in order to power the
sensor device by means of the photoelectric cell or any other solar cell in the sensor
device. For example, during the night and during cloudy days, there is typically not
enough light for powering the device. The required power, e.g. for powering the sensor
in an active mode, may then be provided by the battery.
[0018] There are several reasons for the great power-consumption savings provided by the
inventive method.
[0019] Firstly, required components for the vehicle detection by the photoelectric cell
have a low power-consumption in comparison to the components commonly used, e.g. sensors
such as a magnetometer or an accelerometer. Further, the photoelectric cell has a
wider detection range than a magnetometer or an accelerometer. This allows for the
utilization of the sleep mode and the active mode for the sensor device, in particular
for sensors therein, since the sensors may be given time to start up and prepare for
measuring on the vehicle before the vehicle has reached the sensing zones of the sensors.
Thus, the sensors do not need to consume any power when they are not utilized, i.e.
when no vehicles are passing.
[0020] Secondly, the sample rate may by the inventive method be below 10 Hz, thus the sample
rate may be substantially reduced in comparison to typical sensors. Thus, the power
consumption may be reduced further. The sample rate for e.g. a magnetic sensor is
typically in the order of 50 Hz, and for an accelerometer in the order of several
kHz. The sample rate of the inventive method is only limited to that at least one
sample has to be taken during the time it takes for a vehicle to pass the detection
area of the photoelectric cell. For example, if the detection area is 30 meters, and
the sensor is arranged to detect vehicles having a speed of 110 kilometers per hour,
i.e. approximately 30 meters per second, the photoelectric cell has to measure at
least two times per second in order to detect the vehicle independent of when in the
detection cycle the vehicle passes. In this example, the sample rate may thus be only
2 Hz. In order to cover for other scenarios requiring higher sample rate, or for possible
sensing failures, the sample rate may need to be higher. Preferably, the sample rate
lies within the range of 3-10 Hz.
[0021] Hence, the inventive method provides a great power consumption reduction. The method
may provide advantages such as extending the lifetime of the sensor device and alleviating
the need for frequent battery changes. A sensor device may be provided which may function
continuously night and day with a low average power consumption.
[0022] The method may comprise that a plurality of sensors are activated by the controller.
The sensors in the vehicle sensor device may for example be magnetic sensors, accelerometers,
optical sensors, acoustic sensors, microphones, or a combination thereof. The vehicle
sensor device may comprise a combination of different sensor types. The one or more
sensors may be utilized for functions such as vehicle speed estimation, vehicle classification,
and/or other measurements on the vehicle.
[0023] The method may further comprise activating a timer in connection to the activation
of the sensor, wherein the sensor is deactivated by the controller when the timer
reaches a predetermined timeout value, thereby setting the vehicle sensor device in
the sleep mode.
[0024] Thus, the vehicle sensor device goes into its sleep mode when the one or more sensors
therein are passive, i.e. when there are no vehicles present for the sensors to measure
on. However, the photoelectric cell is always active for receiving any incoming light.
When the photoelectric cell receives light assumed to be provided by a light source
on a vehicle, the sensors are activated again. Very low power consumption may be achieved
when the sensors are consuming power only during their measurements and not during
the lapsed time between the measurements.
[0025] The vehicle sensor device is preferably arranged in or adjacent to a roadway.
[0026] The method may further comprise, provided that the strength of the input signal is
above a predetermined charging threshold value, charging a battery by a solar cell,
the battery being arranged to power the vehicle sensor device.
[0027] Thus, the battery may be charged during periods when there is sufficient daylight,
and utilized during periods when there is not sufficient daylight for charging or
powering the device by the solar cell. Since the vehicle sensor device may shift between
the active mode and the sleep mode, the battery may power the device during a longer
period without the need for charging in comparison with known techniques.
[0028] The solar cell may also be utilized to power the vehicle sensor device when there
is provided sufficient light. The vehicle sensor device may be arranged such that
it shifts between the active mode and the sleep mode only when the there is not sufficient
light provided to the solar cell in order to power the device, i.e. when the device
must be powered by the battery.
[0029] The solar cell and the photoelectric cell may be the same cell, i.e. the photoelectric
cell may be utilized both for charging the battery, powering components of the vehicle
sensor device, and for detecting a vehicle.
[0030] The light source may be a headlight of a vehicle, in particular a headlight of an
vehicle approaching the vehicle sensor device.
[0031] According to a second aspect of the invention, this and other objects are achieved
by a vehicle sensor device operable between a sleep mode and an active mode, the vehicle
sensor device comprising: a photoelectric cell; a controller; and at least one sensor;
wherein the photoelectric cell is arranged to generate, when the vehicle sensor device
is in the sleep mode and when the photoelectric cell receives light, an input signal
by the photoelectric cell; whereby the at least one sensor in the vehicle sensor device
is arranged to be activated by the controller, provided that the input signal lies
within a predetermined interval and thereby assuming that at least a part of the received
light is provided by a light source on a vehicle, thereby setting the vehicle sensor
device in the active mode.
[0032] At least one of the sensors may be one of, or a combination of, the following sensor
types: a magnetic sensor, an accelerometer, an optical sensor, an acoustic sensor,
or a microphone.
[0033] The vehicle sensor device may further comprise a timer which is arranged to be activated
in connection to the activation of the sensor, wherein the at least one sensor is
arranged to be deactivated by the controller when the timer reaches a predetermined
timeout value, thereby setting the vehicle sensor device in the sleep mode.
[0034] The vehicle sensor device may further comprise an amplifier. The amplifier may be
arranged to amplify the input signal. The amplifier may be an operational amplifier.
[0035] The vehicle sensor device may be arranged in or adjacent to a roadway.
[0036] The vehicle sensor device may further comprise a battery, wherein the vehicle sensor
device is arranged to, when the input signal is above a predetermined charging threshold
value, charge the battery by a solar cell, the battery being arranged to power the
vehicle sensor device.
[0037] The solar cell may be the photoelectric cell.
[0038] The vehicle sensor device may further comprise a wireless communicator, such as a
radio transmitter.
[0039] Thus, the above disclosed features and corresponding advantages of the first aspect
is also applicable to this second aspect. To avoid undue repetition, reference is
made to the discussion above.
[0040] It is noted that the invention relates to all possible combinations of features recited
in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] This and other aspects of the present invention will now be described in more detail,
with reference to the enclosed drawings showing embodiments of the invention.
Figure 1 illustrates a vehicle sensor device.
Figure 2 illustrates the vehicle sensor device by a roadway on which a vehicle is
travelling.
Figure 3 illustrates a method for operating the vehicle sensor device.
[0042] The figures are adapted for illustrative purposes and, thus, they are provided to
illustrate the general concept of embodiments of the present invention. Like reference
numerals refer to like elements throughout.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0043] The present invention will now be described more fully hereinafter with reference
to the accompanying drawings, in which currently preferred embodiments of the invention
are shown. This invention may, however, be embodied in many different forms and should
not be construed as limited to the embodiments set forth herein; rather, these embodiments
are provided for thoroughness and completeness, and for fully conveying the scope
of the invention to the skilled person.
[0044] A vehicle sensor device 1 is illustrated in figure 1. The vehicle sensor device 1
comprises a solar cell 10 which is connected to an amplifier 11 and a battery 16.
[0045] The vehicle sensor device 1 further comprises an amplifier 11, which in in this embodiment
is an operational amplifier. The amplifier 11 is connected to an A/D converter 12
such that an amplified signal may be A/D converted.
[0046] The A/D converter 12 may be an A/D converter with a resolution of about 10-16 bits,
or be a high resolution A/D converter, with a resolution of about 18-24 bits. In one
embodiment, where the A/D converter 12 is a high resolution A/D converter. the vehicle
sensor device 1 does not comprise an amplifier 11, and thus the solar cell 10 is directly
connected to the high resolution A/D converter. Thus, the present invention may be
achieved without an amplifier and the measurement of the strength of the input signal
may be performed directly on the non-amplified input signal.
[0047] A measurement on the amplified input signal is more easily implemented and thus preferred.
Therefore, in the embodiment disclosed hereafter in connection to the figures, the
amplifier 11 is arranged between the solar cell 10 and the A/D converter 12. The output
signal from the A/D converter 12 may be transmitted to a controller 13. The controller
13 is arranged to control the one or more sensors of the vehicle sensor device 1.
In this embodiment, the vehicle sensor device 1 has two sensors: a magnetometer 14
and an accelerometer 15. The controller 13 controls the sensors by e.g. activating
and deactivating them. In this embodiment, the controller 13 is a micro controller.
[0048] The A/D converter may be part of the controller 13.
[0049] The controller 13 comprises a processor 18. The processor 18 may be arranged to analyze
the output signal from the A/D converter 12. The controller 13 further comprises a
memory 19. The memory 19 may store data which is e.g. predetermined or generated during
measurements.
[0050] The vehicle sensor device 1 further comprises a wireless communicator 17 for communicating
data from the vehicle sensor device 1 to other devices, such as another similar vehicles
sensor device 1. The wireless communicator 17 may be controlled by the controller
13. The wireless communicator 17 is not a necessary component in order to achieve
the present invention. However, the wireless communicator 17 is preferably included
in the vehicle sensor device 1 for further reducing the need for time-consuming a
costly service of the device 1. Instead of manually extracting data from the vehicle
sensor device 1, the data may be transmitted to a service center or another vehicle
sensor device 1.
[0051] It is noted that the connections may be direct or indirect connections, and that
there may also be provided other connections between the components.
[0052] The vehicle sensor device 1 is arranged such that its components may be powered either
directly by the solar cell 10, by another solar cell of the vehicle sensor device
1, or by the battery 16.
[0053] The solar cell 10 is a photoelectric cell arranged to receive light, thereby producing
an electric signal with a voltage level depending on how much light the photoelectric
cell receives. The vehicle sensor device 1 may comprise a plurality of photoelectric
cells, i.e. solar cells, which may form one or more solar-cell panels. The solar cell
10 may be connected to a terminal box for a solar-cell panel which transmits the electric
signal of the solar cell 10 to the amplifier 11. The electric signal of the solar
cell 10 may be a part of a total electric signal comprising electric signals from
a plurality of solar cells of the solar-cell panel.
[0054] Figure 2 illustrates the vehicle sensor device 1 arranged by a roadway 23. A vehicle
20 is travelling on the roadway 23 in a direction towards the vehicle sensor device
1. The vehicle sensor device 1 is arranged to detect the vehicle 20 by means of the
solar cell 10. Upon detection, the vehicle sensor device 1 is set in an active mode
by activating the magnetometer 14 and accelerometer 15 therein. The detection and
activation method is illustrated in figure 3, and will be described in detail in the
following.
[0055] The headlight of the vehicle 20 is directed towards the vehicle sensor device 1,
and the solar cell 10 is arranged such that it may receive light from the headlight.
When the light from the headlight of the vehicle is received by the solar cell 10,
an input signal, being an electric signal, is generated by the solar cell 10, as denoted
by 301 in figure 3. The electric signal of the solar cell 10 is hereafter referred
to as input signal. The input signal is provided to the amplifier 11, which amplifies
the input signal, denoted by 302 in figure 3. Thereafter, the strength of the input
signal is determined.
[0056] The value of the input signal may be determined in many ways which are known in the
art. In this embodiment, the input signal is amplified, by the amplifier 12, and A/D
converted, by the A/D converter 12, in order to digitally process the converted input
signal. Software is utilized to process the converted input signal and to determine
its value. Based on the strength of the input signal, the software may initiate further
action such as an activation of the sensors in the vehicle sensor device 1. The software
may be part of the processor 18 and/or the controller 13.
[0057] In an alternative embodiment, the input signal, or the amplified input signal, is
processed by a voltage detector or a voltage comparator. Thus, the determination may
alternatively be hardware implemented. Based on the strength of the input signal,
the voltage detector or voltage comparator may initiate further actions such as instructing
the controller 13 to activate the sensors in the vehicle sensor device 1.
[0058] In one embodiment, the controller 13, and in particular the processor 18, may analyze
the A/D converted input signal by e.g. applying processing algorithms. Thus, the input
signal, or a processed signal thereof, may be evaluated, besides from being evaluated
in respect to its strength, in order to more securely determine that the received
light originates from the vehicle 20.
[0059] If the input signal lies within a predetermined interval, it is assumed that at least
a part of light received by the solar cell 10 is provided by a light source on a vehicle
which in this embodiment is the headlight of the vehicle 20. Thereupon, the vehicle
sensor device is activated, as denoted by 303 in figure 3. Two examples of detection
scenarios will be disclosed in the following.
[0060] In the first detection scenario, the surrounding light is substantially zero, as
it may be for example by night when a single vehicle 20 passes by the vehicle sensor
device 1. Thus, the input signal originates substantially from the headlight of the
vehicle 20. The predetermined interval may in this scenario be set to a fixed interval
comprising the voltage values of the input signal, which is expected to be obtained
by a typical light source on a single vehicle within a sensing range of the solar
cell 10. For example, the input signal may have a voltage level in a range of 0.1-1
mV, if it substantially originates from the light source of the vehicle 20. This interval
is thus the predetermined interval, in which it is to be determined if the input signal
lies within. The amplifier 11 is in this example arranged to amplify the input signal
1000 times. Thus, the amplified input signal will lie in a range of 0.1-1 V. If it
is determined that the input signal lies within the predetermined interval, it is
assumed that the input signal did originate from the light source of the vehicle 20.
By measuring the amplified input signal and determining if it lies within the amplified
predetermined interval, i.e. 0.1-1 V, it may be determined that the input signal lies
within the predetermined interval.
[0061] In the second detection scenario, the surrounding daylight is not substantially zero,
as it is for example by day. Thus, only a part of the input signal originates from
the light source of the vehicle 20. The predetermined interval is in this scenario
a flexible interval. The flexible interval is set relative a predetermined strength
level of a solar cell signal, which is generated before generating the input signal.
The predetermined signal strength level may be a mean value over time for the strengths
of signals generated by the solar cell 10, or be the strength of a signal provided
by the solar cell 10 at a particular point of time. Other suitable predetermined signal
strength levels may also be utilized, as realized by the skilled person. The predetermined
signal strength levels may be updated frequently. The predetermined signal strength
level may be stored in the memory 19 of the vehicle sensor device 1.
[0062] The predetermined interval may be set as an interval added to the predetermined signal
strength level. As disclosed in the previous example scenario, the input signal originating
substantially from a typical headlight of a single vehicle lies in the range of 0.1-1
mV. If the predetermined signal strength level is for example 1.6 mV, the predetermined
interval may be set to 1.7-2.6 mV. If the strength of the input signal is determined
to lie within this predetermined interval, it is assumed that a part of the input
signal originates from the headlight of the vehicle 20.
[0063] The vehicle sensor device 1 may be arranged to shift between different predetermined
intervals. If the input signal decreases towards 0 V, or decreases below a certain
voltage level, the vehicle sensor device 1 may be arranged to shift from comparing
against a flexible predetermined interval to comparing against a fixed predetermined
interval.
[0064] If the input signal is determined to be greater than a predetermined charging threshold,
the input signal is utilized for charging the battery 16. The predetermined charging
threshold depends on the electronics used. Typically, it lies within 1-5 V. If a Minimum
Power Point Tracking (MPPT) device is utilized, 1 V may be sufficient for charging
the battery 16. If a MPPT is not utilized, the strength of the input signal might
have to be higher than the battery voltage, which may differ between different battery
types. As an example, a lithium polymer battery typically requires a charge voltage
of 4.2 V, while a nickel-metal hydride cell typically only requires 1.2 V.
[0065] Hence, how the vehicle sensor device 1 uses the input signal depends on the strength
of the input signal. Typically, the input signal is utilized for charging the battery
16 and/or directly powering the components of the vehicle sensor device 1 during the
day when the daylight is sufficient for these functions. When the daylight is sufficient
for powering the vehicle sensor device 1, there is no direct need for saving power.
When the daylight is not sufficient for powering the vehicle sensor device 1, the
vehicle sensor device 1 goes into its power-saving mode. In the power-saving mode,
the magnetometer 14 and the accelerometer 15 are deactivated by default. When the
vehicle 20 is detected by means of the solar cell 10, according to the inventive method,
the magnetometer 14 and accelerometer 15 are temporarily activated for performing
further measurements on the vehicle 20. However, the shift between the active mode
and the sleep mode may also be utilized when the daylight is sufficient for powering
the vehicle sensor device 1.
[0066] It should be noted that the input signal may be utilized for a plurality of purposes.
In one embodiment, the input signal may be utilized for charging a battery and, when
it is detected that the input signal lies within a flexible predetermined interval,
also utilized for detecting the vehicle and activating the vehicle sensor device 1.
[0067] The different sensing components of the vehicle sensor device 1 have different sensing
zones, as illustrated in figure 2.
[0068] The first sensing zone 24 is the sensing zone of the solar cell 10. When the vehicle
20 enters the first sensing zone 24, the light received by the solar cell 10 from
the headlight of the vehicle 20 is sufficiently strong in order to be received by
the solar cell 10 and generate an input signal. The first sensing zone 24 reaches
from the vehicle sensor device 1 to about 25-35 meters before and after the vehicle
sensor device 1.
[0069] The second sensing zone 26 is the sensing zone of the magnetometer 14. Within the
second sensing zone 26, the magnetometer 14 is able to sense the vehicle 20 by sensing
its magnetic field or its magnetic impact on surrounding magnetic fields. The measurement
of the magnetometer 14 may for example be utilized for confirming the assumption that
the vehicle 20 is present. The second sensing zone 26 lies within the first sensing
zone 24 and reaches from the vehicle sensor device 1 to about 5-7 meters before and
after the vehicle sensor device 1.
[0070] The third sensing zone 28 is the sensing zone of the accelerometer 15. Within the
third sensing zone 28, the accelerometer 15 is able to sense the vehicle 20 by sensing
vibrations originating from the vehicle 20. The third sensing zone 28 lies within
the second sensing zone 26 and reaches from the vehicle sensor device 1 to about 3-4.5
meters from the vehicle sensor device 1.
[0071] It is noted that the sensing zones are illustrated for the purpose of understanding
the general concept. The sensing zones may in other embodiment have a different extension
area or shape of extension area. However, in preferred embodiments, the first sensing
zone 24 of the solar cell 10 extends at least 20 meters further relative to a sensing
zone of one of the sensors of the vehicle sensor device 1. In particular, it is preferred
that the first sensing zone 24 extends at least 20 meters further relative to a sensing
zone of any of the sensors of the vehicle sensor device 1.
[0072] Since the vehicle sensor device 1 is able to detect the vehicle 20, by means of the
solar cell 10, already when the vehicle 20 enters the first sensing zone 24, the vehicle
sensor device 1 is given time to activate the magnetometer 14 and accelerometer 15.
Thus, the sensors have time to start up and may thus be ready to perform measurements
when the vehicle 20 enters the second sensing zone 26 and the third sensing zone 28.
In known techniques where the magnetometer 14 is utilized for detecting the vehicle,
such activation/start-up time is shorter and may not be sufficient.
[0073] A timer is activated in connection to the activation of the sensors, as denoted by
304 in figure 3. The timer may be implemented in the processor 18. The timer may be
activated at any time during the activation process, e.g. when it is determined that
the input signal lies within the predetermined interval, when the controller activates
a sensor, when a sensor performs a measurement, etc.
[0074] The timer runs until it reaches a predetermined timeout value, whereby the vehicle
sensor device 1 is deactivated. The deactivation involves deactivating the sensors
of the vehicle sensor device 1, i.e. the magnetometer 14 and the accelerometer 15,
such that they are put into a standby mode. The vehicle sensor device 1 is thereby
set in its sleep mode, awaiting the next activation upon detecting a new vehicle by
means of the solar cell 10. The timeout value may be stored in the memory 19.
[0075] The timeout value may be set to a fixed value such as three times the time it takes
for a vehicle with an assumed speed to reach the vehicle sensor device 1. For example,
if it takes two seconds from the detection moment for the vehicle to reach the vehicle
sensor device 1, the timeout value is six seconds. The assumed speed may be e.g. the
speed limit for the concerned roadway.
[0076] Alternatively, the timeout value may be a dynamic value. Depending on factors such
as the allowed speed, roadway conditions, obstacles, dirt, and weather, the passing
vehicles may travel with varying speed over time. The vehicle sensor device 1 may
determine, by the controller 13 and/or the processor 18, the time it takes for a plurality
of vehicles to e.g. first be detected by the solar cell 10 and then by the magnetometer
14. The timeout value may for example be set to three times the mean value for the
passing time of the last twenty vehicles. Thus, the timeout value may change over
time. Other ways for determining the value of the timeout value is also feasible,
as understood by the skilled person.
[0077] In one embodiment, the vehicle sensor device 1 is arranged such that, when the input
signal is below a predetermined deactivation threshold, the one or more sensors of
the vehicle sensor device 1 are deactivated. Thus, the vehicle sensor device 1 goes
from a mode where the vehicle sensor device 1 is activated by default to a mode where
the vehicle sensor device 1 shifts between its active mode and its sleep mode. From
the sleep mode, the one or more sensors are activated and deactivated as disclosed
above. The predetermined deactivation threshold preferably coincides with the predetermined
charging threshold value, such that the device goes into the sleep mode when the input
signal is too weak for charging the battery.
[0078] In summary, this application discloses a method for operating a vehicle sensor device
1 between a sleep mode and an active mode. The method comprises generating 301 an
input signal by the photoelectric cell; and activating 303, provided that the input
signal lies within a predetermined interval, a sensor 14, 15 in the vehicle sensor
device, thereby setting the vehicle sensor device 1 in the active mode. The application
further discloses a vehicle sensor device 1 comprising a photoelectric cell 10, a
controller 13, and at least one sensor 14, 15. The components are arranged to perform
the method for operating the vehicle sensor device 1 between the sleep mode and the
active mode.
[0079] It is understood that these embodiments may be combined or altered during different
periods. For example, a fixed predetermined interval may be utilized when the input
signal lies below a certain level, whereas a flexible predetermined interval is utilized
when the input signal lies above a certain level.
1. A method for operating a vehicle sensor device (1) between a sleep mode and an active
mode, the method comprising:
generating (301), when the vehicle sensor device is in the sleep mode and when a photoelectric
cell (10) receives light, an input signal by the photoelectric cell; and
activating (303), provided that the input signal lies within a predetermined interval
and thereby assuming that at least a part of the received light is provided by a light
source on a vehicle (20), a sensor (14, 15) in the vehicle sensor device, thereby
setting the vehicle sensor device in the active mode.
2. The method according to claim 1, further comprising, preceding the step of activating,
a step of amplifying (302) the input signal.
3. The method according to claim 2, wherein the sensor is one of, or a combination of,
the following sensor types: a magnetic sensor, an accelerometer, an optical sensor,
an acoustic sensor, or a microphone.
4. The method according to any of the claims 1-3, further comprising activating (304)
a timer in connection to the activation of the sensor, wherein the sensor is deactivated
by the controller when the timer reaches a predetermined timeout value, thereby setting
the vehicle sensor device in the sleep mode.
5. The method according to any of the claims 1-4, wherein the vehicle sensor device is
arranged in or adjacent to a roadway (23).
6. The method according to any of the claims 1-5, wherein the method further comprises,
provided that the strength of the input signal is above a predetermined charging threshold
value, charging a battery (16) by a solar cell, the battery being arranged to power
the vehicle sensor device.
7. The method according to claim 6, wherein the solar cell is the photoelectric cell.
8. A vehicle sensor device (1) operable between a sleep mode and an active mode, the
vehicle sensor device comprising:
a photoelectric cell (10);
a controller (13); and
at least one sensor (14, 15);
wherein the photoelectric cell is arranged to generate, when the vehicle sensor device
is in the sleep mode and when the photoelectric cell receives light, an input signal
by the photoelectric cell;
whereby the at least one sensor in the vehicle sensor device is arranged to be activated
by the controller, provided that the input signal lies within a predetermined interval
and thereby assuming that at least a part of the received light is provided by a light
source on a vehicle, thereby setting the vehicle sensor device in the active mode.
9. The vehicle sensor device according to claim 8, further comprising an amplifier (11),
and wherein the amplifier is arranged to amplify the input signal.
10. The vehicle sensor device according to claim 8 or 9, wherein the at least one sensor
is one of, or a combination of, the following sensor types: a magnetic sensor, an
accelerometer, an optical sensor, an acoustic sensor, or a microphone.
11. The vehicle sensor device according to any of the claims 8-10, further comprising
a timer which is arranged to be activated in connection to the activation of the sensor,
wherein the at least one sensor is arranged to be deactivated by the controller when
the timer reaches a predetermined timeout value, thereby setting the vehicle sensor
device in the sleep mode.
12. The vehicle sensor device according to any of the claims 8-11, wherein the vehicle
sensor device is arranged in or adjacent to a roadway (23).
13. The vehicle sensor device according to any of the claims 8-12, further comprising
a battery (16), wherein the vehicle sensor device is arranged to, when the input signal
is above a predetermined charging threshold value, charge the battery by a solar cell,
the battery being arranged to power the vehicle sensor device.
14. The method according to claim 13, wherein the solar cell is the photoelectric cell.
15. The vehicle sensor device according to any of the claims 8-14, further comprising
a wireless communicator (17).