Device, system, and method for detecting human presence

An embodiment device includes an optical source configured to transmit an optical pulse and an optical sensor configured to receive a reflection of the optical pulse. The device further includes a processor configured to determine a parameter based on the reflection, the parameter indicative of a distance between the device and a target; and a controller configured to generate a first control signal based on the parameter, the first control signal being configured to control an operation of the optical source.

TECHNICAL FIELD

The present disclosure relates generally to detection of objects in an environment, and, in particular embodiments, to a device, a system, and a method for detecting human presence.

BACKGROUND

Presence detectors may be implemented using a variety of technologies. For example, pneumatic tubes or hoses may be placed across a roadway to detect the pressure of a vehicle as its tires roll over the tubes or hoses. Such detectors operate through physical contact with the object being detected. In another example, an optical light beam emitter and sensor system may detect the presence of an object when the object interrupts a projected light beam. In addition, in-ground inductance loops may detect a vehicle in close proximity by detecting a change in magnetic inductance. Other examples of presence detectors include video detectors and audio detectors.

Time-of-flight (ToF) presence detectors are used in various applications to detect the presence of objects within a specified field of detection. ToF presence detectors generally include one or more optical devices, such as optical emitters and optical sensors, for example. Unlike pneumatic tubes, optical devices in ToF presence detectors do not require physical contact with the item being detected. Unlike inductance loops, optical devices in ToF presence detectors can sense an object regardless of the magnetic properties of the object. Further, unlike a simple optical beam interruption system, ToF detectors can determine the distance between the detector and the object.

ToF presence detectors may be used to detect the presence of an animate object (e.g. a human). Detection of an animate object can be used to detect malicious intrusions in a premises or a protected area, or to ensure that no person is present in a dangerous area before executing a maneuver. Detection of an animate object is also useful in the field of human-machine interaction, where it is desirable to detect the presence of humans in the vicinity of a machine. As an example, ToF presence detectors may be used to detect whether a human is approaching a device (e.g. a computer), and such detection can cause the device to unlock or exit a low-power state in advance of the human making physical contact with the device or a peripheral component (e.g. a mouse or a keyboard) in communication with the device. As a further example, ToF presence detectors may be used to detect whether a human has exited a sensor detection area, and such detection can cause the device to turn off, enter a low-power state, or enter a locked mode (e.g. for security reasons).

Current ToF presence detectors may suffer from false positives, where the detector is unable to distinguish a dormant animate object (e.g. a stationary or immobile human) from an inanimate object (e.g. a chair). Consequently, there may be a need for improved ToF presence detectors that minimize or substantially eliminate such false positives.

SUMMARY

In an embodiment, a device includes an optical source configured to transmit an optical pulse and an optical sensor configured to receive a reflection of the optical pulse. The device further includes a processor configured to determine a parameter based on the reflection, the parameter indicative of a distance between the device and a target; and a controller configured to generate a first control signal based on the parameter, the first control signal being configured to control an operation of the optical source.

In an embodiment, a method includes transmitting, using an optical source, a plurality of optical pulses; receiving, using an optical sensor, a plurality of reflections, each reflection being a reflection of a corresponding optical pulse off a target. The method further includes determining, using a processor, a parameter based on the plurality of reflections, the parameter indicative of a distance between the optical source and the target; and controlling an operation of the optical source based on a comparison of the parameter against a plurality of thresholds.

In an embodiment, a system includes a presence detector and an electronic device coupled to the presence detector. The presence detector may include an optical source configured to transmit an optical pulse, and an optical sensor configured to receive a reflection of the optical pulse. The presence detector may further include a processor configured to determine a parameter based on the reflection, the parameter indicative of a distance between the presence detector and a target; and a controller configured to generate a first control signal based on the parameter, the first control signal being configured to control an operation of the optical source.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of various embodiments are discussed in detail below. It should be appreciated, however, that the various embodiments described herein are applicable in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use various embodiments, and should not be construed in a limited scope.

An embodiment device and an embodiment method of detecting human presence minimize or substantially eliminate such false positives. The embodiment device and the embodiment method are configured to detect small movements (e.g. micro-variations in distance) that occur within a detection area of a presence detector. Detection of such micro-variations in distance may be sufficient to detect small movements (e.g. human breathing) of a dormant animate object, and thus the embodiment device and the embodiment method may be able to discriminate between a stationary inanimate object and a dormant animate object. In response to a determination that micro-variations in distance are present in the detection area of the presence detector, the embodiment device may cause an electronic device to remain in an active state so that the dormant animate object may continue using the electronic device without interruption. On the other hand, in response to a determination that micro-variations in distance are absent in the detection area of the presence detector, the embodiment device may cause the electronic device to switch from the active state to a low-power state, thereby conserving power of the electronic device. Furthermore, high accuracy ranging and micro-variation detection may consume a large amount of power, and thus, according to some embodiments, such ranging and detection is performed when both a parametric threshold and a temporal threshold are met in order to allow for efficient consumption of power by the presence detector.

FIG. 1shows a presence detection system100, in accordance with an embodiment. The presence detection system100includes a presence detector102, an electronic device104, an inanimate object106, and an animate object108. In some embodiments, the presence detector102may be included in, mounted on, or integrated with the electronic device104. In some embodiments, the presence detector102may be electrically and communicatively coupled to the electronic device104. As an example, the presence detector102may be configured to generate a control signal that may cause the electronic device104to switch between a low-power state (e.g. a sleep mode) and an active state (e.g. a wake-up mode). In the example ofFIG. 1, the electronic device104is depicted as a computer screen or monitor. However, other electronic devices104may be possible in other embodiments. As an example, the electronic device104may be a laptop or a mobile device having the presence detector102included therein or mounted thereon.

The presence detector102may be configured to detect objects within a detection area110. The range, extent, and coverage area of the detection area110may depend, at least in part, on the circuitry of the presence detector102. As an example, the detection area110may extend up to about 2 meters from the presence detector102. The presence detector102may be a ToF presence detector that may be used in ToF ranging for various applications such as autofocus, proximity sensing, and object detection in robotics, drone technology, and internet-of-things (IoT) applications. ToF ranging is described in greater detail below in respect ofFIG. 2.

The animate object108may be an object capable of motion without the assistance of an external force. For example, a person or an animal may be the animate object108. In contrast, the inanimate object106may be object that is not capable of movement without the assistance of an external force. Examples of the inanimate object106may include a mug, box or chair. The animate object108that is not moving is herein distinguished from the inanimate object106by referring to the non-moving or immobile animate object108as a dormant animate object108. The animate object108that is moving is herein distinguished from the inanimate object106and the dormant animate object108by referring to the moving animate object108as an active animate object108.

The inanimate object106may be moved by the animate object108. Since the inanimate object106may be moved by the animate object108, in some embodiments, a moving inanimate object106may be characterized as an active animate object108. For example, a chair or mug being moved by a person may initially be characterized as an active animate object. In such examples, the presence detector102may detect movement in the detection area110and thus determine or infer that an active animate object108may be present in the detection area no. Conversely, after the inanimate object106has ceased moving, the presence detector102may detect no movement in the detection area110and thus determine or infer that a stationary inanimate object106may be present in the detection area110. From this description, it may be seen that the presence detector102may be able to discriminate between a stationary inanimate object106and an active animate object108by detecting gestures or macro-variations in movement that occur in the detection area110.

However, there is still a need for the presence detector102to discriminate between a stationary inanimate object106and a dormant animate object108. For example, by being able to discriminate between a stationary inanimate object106and a dormant animate object108, the electronic device104may be able to remain in the active state even when a dormant animate object108is present in the detection area110. A method for discriminating between a stationary inanimate object106and a dormant animate object108may be to configure the presence detector102to detect micro-variations in movement that occur in the detection area no. Such micro-variations in movement may be detected when a dormant animate object108is present in the detection area110(e.g. due to chest movement caused by respiration or small variations in posture and position). On the other hand, such micro-variations in movement may not be detected when a stationary inanimate object106(e.g. a chair or a mug) is present in the detection area110. Embodiments of methods that allow the presence detector102to detect such micro-variations in movement are presented hereafter.

FIG. 2shows a simplified block diagram of the presence detector102and a target202, in accordance with an embodiment. As described above, the presence detector102may be a ToF presence detector that may be used in ToF ranging for various applications such as autofocus, proximity sensing, and object detection in robotics, drone technology, and internet-of-things (IoT) applications. The presence detector102may include an optical source102aand an optical sensor102b. The optical source102amay be configured to generate and emit (or transmit) a burst or pulse of optical energy. The transmission of the optical pulse by the optical source102ais indicated inFIG. 2as transmitted optical pulse201. In some embodiments, the optical source102amay include one or more laser diodes that emit light (e.g. infrared or visible light) in response to a control signal provided to the one or more laser diodes. In an embodiment where the optical source102aincludes a plurality of laser diodes, the plurality of laser diodes may be arranged in an array of laser diodes. In some embodiments, the optical energy generated by the optical source102amay be a short duty cycle pulse train, as discussed below in respect ofFIGS. 3 and 4. In some embodiments, the optical source102amay include vertical-cavity surface-emitting lasers (VCSELs), quantum well lasers, quantum cascade lasers, interband cascade lasers, and vertical external-cavity surface-emitting lasers (VECSELs), although other types of optical sources may be possible in other embodiments.

When the burst or pulse of optical energy generated by the optical source102encounters the target202(e.g. the animate object108and/or the inanimate object106), at least a portion of the energy of the pulse is reflected back to the presence detector102. The reflection of the transmitted optical pulse201back to the presence detector102is indicated inFIG. 2as optical reflection203. The optical sensor102bmay be configured to convert the reflected optical signal203into an electrical pulse. The electrical pulse produced may be a digital pulse output or an analog pulse output, depending on the circuitry of the optical sensor102b.

In an embodiment, the optical sensor102bincludes one or more optical elements, which may include one or more photo diodes (PDs), one or more avalanche photo diodes (APDs), one or more single-photon avalanche diodes (SPADs), or a combination thereof. In an example where the optical sensor102bincludes a plurality of such optical elements (e.g. PDs, APDs, SPADs), the optical elements may be arranged as a sensing array for receiving the optical reflection203. Each of the optical elements of the optical sensor102bmay be configured to output an electrical pulse in response to receiving the optical reflection203. In some embodiments, the optical sensor102bmay additionally include a filter for blocking light outside a predetermined range of frequencies (e.g. light outside the infra-red range) from reaching the sensing array.

The electrical pulse generated by each of the optical elements of the optical sensor102bmay be processed by a processor204. In the embodiment shown inFIG. 2, the processor204is included in the presence detector102. However, in other embodiments, the processor204may be included in the electronic device104. The processor204may be configured to determine the time elapsed between transmission of the optical pulse201and reception of the optical reflection203. The time elapsed may be encoded in a positive edge or a negative edge of the electrical pulse generated by each of the optical elements of the optical sensor102b. The time elapsed may be called a time-of-flight measurement, and the distance between the presence detector102and the target (e.g. the stationary inanimate object106and/or the dormant animate object108) may be calculated, by the processor204, based upon the time-of-flight measurement. For example, a distance D (indicated inFIG. 2) between the presence detector102and the target202may be estimated from the product of the speed of light (which makes a 1 cm round-trip in 67 ps) and one-half of the time-of-flight measurement. An advantage of using optical energy to estimate the distance D is that a direct distance measurement, independent of size, color, or reflectance of the target202, may be made. Additionally, such a distance measurement may be obtained expeditiously (e.g. in about 10 milliseconds).

Since each of the optical elements of the optical sensor102bmay generate an electrical pulse that is subsequently processed by the processor204, the estimate of the distance D between the presence detector102and the target202may be a plurality of distance estimates D1, D2, . . . , Dx, where x is the number of consecutive measurements used to estimate the distance D. The plurality of distance estimates D1, D2, . . . , Dx may have a mean distance Dmeanand a standard deviation σ. In some embodiments, the processor204may determine the mean distance Dmeanand the standard deviation σ of the plurality of distance estimates D1, D2, . . . , Dx. The processor204may further determine a parameter206from the plurality of distance estimates D1, D2, . . . , Dx. As an example, the parameter206may be determined from the mean distance Dmeanand the standard deviation σ of the plurality of distance estimates D1, D2, . . . , Dx. In some embodiments, a ratio of the standard deviation σ and the mean distance Dmean, expressed as a percentage, may be the parameter206determined by the processor204.

The presence detector102may include a controller208, which may receive the parameter206from the processor204. Although the controller208and the processor204are depicted as separate blocks in the example ofFIG. 2, the controller208and the processor204may be implemented by the same electronic component in other embodiments. The controller208may use the parameter206to detect macro-variations (e.g. variations in a range of about 5 centimeters to about 10 centimeters) and micro-variations (e.g. variations less than macro-variations, such as in a range of about 1 millimeter to about 2 millimeters) in the distance D between the target202and the presence detector102, thereby allowing discrimination between a stationary inanimate object106(e.g. a chair or a mug) and a dormant animate object108(e.g. a substantially stationary human user of a computer who generates micro-variations in distance due to respiration). The method executed by the controller208to discriminate between macro-variations and micro-variations in the distance D is discussed in further detail below in respect ofFIG. 5. In particular, as described below in respect ofFIG. 5, macro-variations in the distance D may be detected when the presence detector102is in a standard ranging mode, while micro-variations in the distance D may be detected when the presence detector102is in a high accuracy ranging mode.

The controller208may be configured to vary the operation of the presence detector102(e.g. the optical source102a). As an example, the controller208may be configured to control the operation of the optical source102aby a first control signal210. The first control signal210may vary the time duration during which a distance measurement is performed and the period of time between consecutive distance measurements. Stated in another way, the first control signal210may vary the length of time for which each optical pulse201is transmitted and the length of time between consecutive transmissions of the optical pulse201. Varying these timings may cause the presence detector102to switch among a plurality of modes, and each mode of the presence detector102may be configured to detect either a macro-variation or a micro-variation in the distance D. The plurality of modes of the presence detector102and how each mode is configured to detect either a macro-variation or a micro-variation in the distance D is discussed in further detail below in respect ofFIG. 4.

The controller208may further be configured to vary the operation of the electronic device104based on whether a macro-variation or a micro-variation in the distance D is detected. As an example, the controller208may be configured to control the operation of the electronic device104by a second control signal212. The second control signal212may cause the electronic device104to switch between a low-power state (e.g. a sleep mode) and an active state (e.g. a wake-up mode). For example, in response to a determination that a macro-variation or a micro-variation in the distance D is detected, the second control signal212may prevent the electronic device104from switching from the active state to the low-power state. This example may illustrate the situation where it is desirable that the electronic device (e.g. a computer) does not enter a sleep mode when either a gesturing human or an immobile human is located in the detection area110of the presence detector102. On the other hand, in response to a determination that a micro-variation in the distance D is not detected, the second control signal212may cause the electronic device104to switch from the active state to the low-power state, thereby reducing power consumption by the electronic device104. This example may illustrate the situation where it is desirable that the electronic device104(e.g. a computer) enter a sleep mode when an empty chair is located in the detection area110of the presence detector102. As an illustration of energy savings that are possible, continuous ranging by the presence detector102(e.g. at a ranging frequency of about 10 Hz) may consume about 0.02 Watts. However, a tablet device consumes about 8 Watts in the active state and about 0.4 Watts in the low-power state, while a laptop computer consumes about 80 Watts in the active state, about 20 Watts when its display is turned off, and about 1 Watt when it is in the low-power state.

FIG. 3shows a timing diagram300that illustrates a plurality of distance measurements (labeled as Measurement1to Measurement x) performed in each of a first monitoring period M1and a second monitoring period M2, in accordance with an embodiment. As shown inFIG. 3, each measurement in each monitoring period has a first time duration T1during which a distance measurement is performed, and a second time duration T2that denotes the period of time between consecutive distance measurements. Each of the above-described ToF measurements is performed during the first time duration T1, which may be referred to as a timing budget. The second time duration T2may be referred to as a ranging period. As depicted inFIG. 3, during the first monitoring period M1, a first distance measurement may be performed during the first T1seconds of the first T2seconds block; a second distance measurement may be performed during the first T1seconds of the second T2seconds block; and so on. Similarly, during the second monitoring period M2, a first distance measurement may be performed during the first T1seconds of the first T2seconds block; a second distance measurement may be performed during the first T1seconds of the second T2seconds block; and so on. In some embodiments, a plurality of distance estimates D1, D2, . . . , Dx having a mean distance Dmeanand a standard deviation σ is generated for each monitoring period. As such, detection of variations in movement may be accomplished in each of the monitoring periods M1and M2. In some embodiments, about 10 measurements may be performed in each of the first monitoring period M1and the second monitoring period M2(e.g. such that x is equal to about 10). Illustratively, the first monitoring period M1may be used for macro-variation monitoring, while the second monitoring period M2may be used for macro- and micro-variation monitoring. Stated differently, the presence detector102may be configured to determine, in the first monitoring period M1, whether macro-variations in movement occur within the detection area110, and to determine, in the second monitoring period M2, whether macro- and micro-variations in movement occur within the detection area110. As depicted inFIG. 3, the first time duration T1may vary from one monitoring period to the next. In the example shown inFIG. 3, the first time duration T1in the second monitoring period M2is greater than the first time duration T1in the first monitoring period M1. As an example, the first time duration T1in the first monitoring period M1may be about 33 milliseconds, while the first time duration T1in the second monitoring period M2may be about 1 second. As described below in respect ofFIG. 4, this may be an effect of the first monitoring period M1being used for macro-variation monitoring and the second monitoring period M2being used for macro- and micro-variation monitoring.

FIG. 4shows various operating modes of the presence detector102relative to the first time duration T1and the second time duration T2, in accordance with an embodiment. The vertical axis denotes the first time duration T1(e.g. the timing budget) measured in arbitrary units of time. The horizontal axis denotes the inverse of the second time duration T2measured in arbitrary units of frequency (e.g. Hertz). In some embodiments, the inverse of the second time duration T2may be referred to as a ranging frequency. As depicted inFIG. 4, the ranging frequency may be in a first frequency range FR1or a second frequency range FR2. The first frequency range FR1and the second frequency range FR2may be non-overlapping frequency ranges. In some embodiments, the first frequency range FR1may be between about 10 Hz and about 120 Hz (for fast gesture detection). As an example, the ranging frequency may be about 50 Hz (e.g. where the second time duration T2is about 20 ms) when in the first frequency range FR1. On the other hand, the second frequency range FR2may be between about 0.5 Hz and about 10 Hz. As an example, the ranging frequency may be about 1 Hz (e.g. where the second time duration T2is about 1 s) when in the second frequency range FR2.

Referring now to the first time duration T1depicted inFIG. 4, the first time duration T1may be in a first time range TR1or a second time range TR2. The first time range TR1and the second time range TR2may be non-overlapping time ranges. In some embodiments, the first time range TR1may be between about 0.5 s and about 2 s. As an example, the first time duration T1may be about 1 s when in the first time range TR1. On the other hand, the second time range TR2may be between about 16 ms and about 100 ms. As an example, the first time duration T1may be about 20 ms when in the second time range TR2.

When the first time duration T1is in the second time range TR2(e.g. equal to about 20 ms) and the ranging frequency is in the first frequency range FR1(e.g. equal to about 50 Hz), the presence detector102may be in a first mode, as depicted inFIG. 4. When in the first mode, the presence detector102may be configured for high-speed ranging (e.g. since the time between consecutive distance measurements is short, such as about 20 ms). When in the first mode, the presence detector102may be able to detect gestures, such as gestures from an active animate object108.

In some embodiments, when the first time duration T1is increased, the accuracy of the estimated distance D increases. As an example, the standard deviation σ of the plurality of distance estimates D1, D2, . . . , Dx (e.g. obtained after a plurality of measurements or ranging periods T2) decreases as the first time duration T1is increased. In some embodiments, increasing the first time duration T1by a factor of N may decrease the standard deviation σ of the plurality of distance estimates D1, D2, . . . , Dx by a factor equal to the square-root of N. As such, when the first time duration T1is in the first time range TR1(e.g. equal to about 1 s), high accuracy ranging may be performed by the presence detector102. Since the second time duration T2is greater than or equal to the first time duration T1, the ranging frequency may be in the second frequency range FR2(e.g. equal to about 1 Hz) when the first time duration T1is in the first time range TR1. Consequently, as shown inFIG. 4, when the first time duration T1is in the first time range TR1(e.g. equal to about 1 s) and the ranging frequency is in the second frequency range FR2(e.g. equal to about 1 Hz), the presence detector102may be in a second mode. When in the second mode, the presence detector102may be configured for high-accuracy ranging (e.g. since the first time duration T1is increased). When in the second mode, the presence detector102may be able to determine whether micro-variations in movement occur within the detection area110. Additionally, in some embodiments, the presence detector102, in the second mode, may be able to determine whether macro-variations in movement occur within the detection area110.

When the first time duration T1is in the second time range TR2(e.g. equal to about 20 ms) and the ranging frequency is in the second frequency range FR2(e.g. equal to about 1 Hz), the presence detector102may be in a third mode, as depicted inFIG. 4. When in the third mode, the presence detector102may be configured for low-power ranging (e.g. since the optical energy generated by the optical source102ais a short duty cycle pulse train). When in the third mode, the presence detector102may be able to determine whether macro-variations in movement occur within the detection area110.

The power consumption associated with each of the modes of the presence detector102may be different. In some embodiments, the presence detector102may derive its power from the electronic device104or from the same source as the electronic device104. The power consumed by the presence detector102when the presence detector102is in the first mode is greater than the power consumed when the presence detector102is in the second mode or the third mode. This may be due to the fact that the first time duration T1is increased (e.g. to about 1 second) and the optical pulse201is continuously transmitted during this increased period of time. However, the power consumed by the presence detector102when the presence detector102is in the third mode may be less than the power consumed when the presence detector102is in the first mode or the second mode. This may be due to the fact that the first time duration T1is decreased (e.g. to about 20 ms), while the time between distance measurements is increased (e.g. to about r second), thereby resulting in a short duty cycle pulse train. In light of the relative power requirements associated with the first mode, the second mode, and the third mode of the presence detector102, it may be desirable to switch the presence detector102to the second mode (e.g. the high-power mode) infrequently or after a certain threshold is met. This is discussed in further detail below in respect ofFIG. 5.

FIG. 5shows a flow chart illustrating a method500of determining macro-variations and micro-variations in the distance D, in accordance with an embodiment. As shown in the flow chart, the method500is initiated by placing the presence detector102in the first mode and by having the electronic device104in the active state (in step502). For example, the controller208, using the first control signal210, may set the first time duration T1to be in the second time range TR2(e.g. equal to about 20 ms) and the ranging frequency to be in the first frequency range FR1(e.g. equal to about 50 Hz). Additionally, in step502, the controller208, using the second control signal212, may cause the electronic device104to remain in the active state. In the first mode, the presence detector102is configured to perform high speed ranging and gesture detection, as described above in relation toFIG. 4. Such high speed ranging and gesture detection generates parameter206, which is provided to the controller208by the processor204.

The method500includes determining (e.g. by the controller208) whether the parameter206(generated while the presence detector102is in the first mode and the electronic device104is in the active state) is less than a first parametric threshold (in step504). As described above, the parameter206may be the ratio of the standard deviation σ and the mean distance Dmean, expressed as a percentage. In such an embodiment, the first parametric threshold may be between about 5 percent and about 20 percent (e.g. about 10 percent). The parameter206being greater than the first parametric threshold may be indicative of macro-variations and/or gesture activity in the detection area110, and thus there may not be a need to cause the electronic device104to switch from the active state to the low-power state. In such a scenario, the method500proceeds from step504back to step502. On the other hand, the parameter206being less than the first parametric threshold may be indicative of a reduced amount of macro-variations and/or gesture activity in the detection area110. In such a scenario, the method500proceeds from step504to step506.

In step506of method500, the controller208may determine whether the parameter206has been less than the first parametric threshold for an extended period of time. As such, the duration of time during which the parameter206has been less than the first parametric threshold is compared against a first temporal threshold. In some embodiments, the first temporal threshold may be between about 3 seconds and about 8 seconds (e.g. about 5 seconds). The parameter206being greater than the first parametric threshold for any time during the first temporal threshold may indicate that the reduced amount of macro-variations and/or gesture activity in the detection area110has not persisted for an extended period of time. Thus, there may not be a need to cause the electronic device104to switch from the active state to the low-power state. In such a scenario, the method500proceeds from step506back to step502. On the other hand, the parameter206being less than the first parametric threshold for longer than the first temporal threshold (e.g. longer than about 5 seconds) may indicate that the reduced amount of macro-variations and/or gesture activity in the detection area110has persisted for an extended period of time. This may indicate the presence of either a dormant animate object108or a stationary inanimate object106in the detection area110. As such, there may be a need to determine whether micro-variations in distance are occurring in order to discriminate between a dormant animate object108and a stationary inanimate object106. In such a scenario, the method500proceeds from step506to step508.

In step508of method500, the presence detector102is placed in the second mode and the electronic device104remains in the active state. For example, the controller208, using the first control signal210, may set the first time duration T1to be in the first time range TR1(e.g. equal to about 1 s) and the ranging frequency to be in the second frequency range FR2(e.g. equal to about 1 Hz). Additionally, in step508, the controller208, using the second control signal212, may cause the electronic device104to remain in the active state. In the second mode, the presence detector102is configured to perform high accuracy ranging and micro-variation detection, as described above in relation toFIG. 4. Consequently, the presence detector102enters the second mode (e.g. in step508) when both a parametric threshold and a temporal threshold are met. In essence, high accuracy ranging and micro-variation detection (which consumes more power relative to the first mode and the third mode) is performed when a reduced amount of macro-variations and gesture activity in the detection area110has persisted for an extended period of time. This allows for efficient consumption of power by the presence detector. Such high accuracy ranging and micro-variation detection generates parameter206, which is provided to the controller208by the processor204.

The method500includes determining (e.g. by the controller208) whether the parameter206(generated while the presence detector102is in the second mode and the electronic device104is in the active state) is less than a second parametric threshold (in step510). The second parametric threshold is less than the first parametric threshold. As described above, the parameter206may be the ratio of the standard deviation σ and the mean distance Dmean) expressed as a percentage. In such an embodiment, the second parametric threshold may be between about 0.1 percent and about 0.5 percent (e.g. about 0.2 percent). The parameter206being greater than the second parametric threshold may be indicative of micro-variations of the distance D in the detection area110, and thus there may not be a need to cause the electronic device104to switch from the active state to the low-power state since a dormant animate object108may be present in the detection area110. In such a scenario, the method500proceeds from step510back to step502. On the other hand, the parameter206being less than the second parametric threshold may be indicative of the absence micro-variations of the distance D in the detection area110.

However, for a substantially accurate determination that micro-variations of the distance D are absent in the detection area110, in step511of method500, the controller208may determine whether the parameter206has been less than the second parametric threshold for an extended period of time. As such, the duration of time during which the parameter206has been less than the second parametric threshold is compared against a second temporal threshold. In some embodiments, the second temporal threshold may be greater than the first temporal threshold. As an example, the second temporal threshold may be between about 10 seconds and about 25 seconds (e.g. about 10 seconds or about 20 seconds). The parameter206being greater than the second parametric threshold for any time during the second temporal threshold may indicate that the reduced amount of micro-variations and/or gesture activity in the detection area110has not persisted for an extended period of time. Thus, there may not be a need to cause the electronic device104to switch from the active state to the low-power state. In such a scenario, the method500proceeds from step511back to step502. On the other hand, the parameter206being less than the second parametric threshold for longer than the second temporal threshold (e.g. longer than about 10 seconds) may indicate that the reduced amount of micro-variations and/or gesture activity in the detection area110has persisted for an extended period of time. In such a scenario, it is plausible to infer that no dormant animate object108is present in the detection area110. As such, when the parameter206is less than the second parametric threshold for longer than the second temporal threshold, the method500proceeds from step511to step512.

In step512of method500, the presence detector102is placed in the third mode and the electronic device104is placed in the low-power state. For example, the controller208, using the first control signal210, may set the first time duration T1to be in the second time range TR2(e.g. equal to about 20 ms) and the ranging frequency to be in the second frequency range FR2(e.g. equal to about 1 Hz). Additionally, in step512, the controller208, using the second control signal212, may cause the electronic device104to switch from the active state to the low-power state. In the third mode, the presence detector102is configured to perform low-power ranging and macro-variation detection, as described above in relation toFIG. 4. When such a macro-variation in distance D is detected, an interrupt may be generated (e.g. by the controller208using the second control signal212), thereby causing the electronic device104to switch from the low-power state to the active state and causing the presence detector102to enter the first mode. In this scenario, the method500proceeds from step514to the step502. On the other hand, if no interrupt is received by the electronic device104, this may indicate that no macro-variations of activity occur in the detection area110, and thus, the presence detector102remains in the third mode and the electronic device104remains in the low-power state until an interrupt is received. This scenario is depicted inFIG. 5as the loop between steps514and512.

In summary, the device and method of detecting human presence discussed herein is configured to detect small movements (e.g. micro-variations in distance) that occur within a detection area of a presence detector. Detection of such micro-variations in distance may be sufficient to detect small movements (e.g. human breathing) of a dormant animate object, and thus the device and method of detecting human presence discussed herein may be able to discriminate between a stationary inanimate object and a dormant animate object. In response to a determination that micro-variations in distance are present in the detection area of the presence detector, the presence detector (e.g. a controller included therein) may cause an electronic device to remain in an active state so that the dormant animate object may continue using the electronic device without interruption. On the other hand, in response to a determination that micro-variations in distance are absent in the detection area of the presence detector, the presence detector (e.g. a controller included therein) may cause the electronic device to switch from the active state to a low-power state, thereby conserving power of the electronic device. Furthermore, high accuracy ranging and micro-variation detection may consume a large amount of power, and thus, such ranging and detection is performed when both a parametric threshold and a temporal threshold are met in order to allow for efficient consumption of power by the presence detector.

While the above description has been directed to detecting human presence in front of the presence detector102for the purposes of conserving power in the electronic device104, it is noted that the presence detector102and the method of detecting human presence is not limited to such an application. As an example, the presence detector102and the method500discussed inFIG. 5may be used to detect and/or monitor the breath of a sleeping baby. In such a scenario, method500may be modified such that the electronic device104sounds an alarm to alert caregivers when micro-variations and/or gesture activity (e.g. the baby's breathing) in the detection area110has persisted for an extended period of time.

For example,FIG. 6shows a presence detection system600, in accordance with another embodiment. As depicted inFIG. 6, presence detector102may be communicatively coupled to the electronic device104(e.g. a baby-monitor having a camera). In the example shown inFIG. 6, the electronic device104is attached or mounted to a crib602via a support structure604. However, in other embodiments, the electronic device104may be placed at some distance away from the crib602such that at least a portion of the crib602is located within the detection area110of the presence detector102.

Macro-variations may be detected in the detection area110(e.g. using steps502,504,506of method500). Such macro-variations may be caused by the baby's body movements, such as rolling, crawling, shifting body positions, as examples. Furthermore, micro-variations may also be detected in the detection area110(e.g. using steps508,510, and511of method500). Such micro-variations may be caused by the baby's breathing when the baby is sleeping. The parameter206being greater than the second parametric threshold for any time during the second temporal threshold may indicate that the reduced amount of micro-variations and/or gesture activity in the detection area110has not persisted for an extended period of time. For example, this may indicated that the baby has fallen asleep and is breathing normally. Thus, there may be a need to cause the electronic device104to remain active and not switch to the low-power state so that continued monitoring of the baby may take place. In such a scenario, the method500proceeds from step511back to step502. On the other hand, the parameter206being less than the second parametric threshold for longer than the second temporal threshold (e.g. longer than about 10 seconds) may indicate that the reduced amount of micro-variations and/or gesture activity in the detection area110has persisted for an extended period of time. For example, this may indicate that the baby's breathing has fallen below what is considered as normal depth of breathing. In such a scenario, instead of placing the electronic device104in the low-power state (e.g. indicated inFIG. 5as the transition from step511to512), method500may be modified such that the electronic device104sounds an alarm to alert caregivers to this anomaly in the baby's breathing. As such, the device and method described above may be used to allow for early intervention in cases where a baby's breathing falls below a predetermined threshold that is indicative of normal infant breathing.

In an embodiment, a device includes an optical source configured to transmit an optical pulse and an optical sensor configured to receive a reflection of the optical pulse. The device further includes a processor configured to determine a parameter based on the reflection, the parameter indicative of a distance between the device and a target; and a controller configured to generate a first control signal based on the parameter, the first control signal being configured to control an operation of the optical source.

In an embodiment, a method includes transmitting, using an optical source, a plurality of optical pulses; receiving, using an optical sensor, a plurality of reflections, each reflection being a reflection of a corresponding optical pulse off a target. The method further includes determining, using a processor, a parameter based on the plurality of reflections, the parameter indicative of a distance between the optical source and the target; and controlling an operation of the optical source based on a comparison of the parameter against a plurality of thresholds.

In an embodiment, a system includes a presence detector and an electronic device coupled to the presence detector. The presence detector may include an optical source configured to transmit an optical pulse, and an optical sensor configured to receive a reflection of the optical pulse. The presence detector may further include a processor configured to determine a parameter based on the reflection, the parameter indicative of a distance between the presence detector and a target; and a controller configured to generate a first control signal based on the parameter, the first control signal being configured to control an operation of the optical source.