PASSIVE INFRARED SENSOR OCCUPANCY DETECTOR, MICROCONTROLLER AND METHODS OF OPERATION

Abstract

A device for occupancy detection of a space includes a passive infrared (PIR) sensor having a fixed field of view; an infrared reflector positioned proximate to the PIR sensor for re-directing infrared radiation received from within the space toward the PIR sensor; an electromechanical device coupled to the infrared reflector and operative to alter a pointing angle thereof in response to a control signal; and, detection and control circuitry (or a microcontroller), coupled to the PIR sensor and the electromechanical device, operative to receive a signal from the PIR sensor indicative of motion of a person within the space, and further operative to selectively alter the pointing angle of the infrared reflector, using the electromechanical device, whereby the relative position of the person is shifted within the fixed field of view of the PIR sensor, thereby simulating motion of the person even when stationary.

Claims

1. A device for occupancy detection of a space, comprising: a passive infrared (PIR) sensor having a fixed field of view; an infrared reflector positioned proximate to said PIR sensor for re-directing infrared radiation received from within said space toward said PIR sensor; an electromechanical device coupled to said infrared reflector and operative to alter a pointing angle thereof in response to a control signal; and, detector and controller circuitry, coupled to said PIR sensor and said electromechanical device, operative to receive a signal from said PIR sensor indicative of motion of a person within said space, and further operative to selectively alter said pointing angle of said infrared reflector, using said electromechanical device, whereby the relative position of said person is shifted within said fixed field of view of said PIR sensor, thereby simulating motion of said person even when stationary.

2. The device recited in claim 1, wherein a nominal pointing angle of said infrared reflector is 45 degrees from the line normal to said PIR sensor.

3. The device recited in claim 1, wherein selectively altering said pointing angle of said infrared reflector comprises periodically panning said infrared reflector in a first direction away from a nominal pointing angle if motion of said person has not been detected for a predefined wait time.

4. The device recited in claim 3, wherein, if panning said infrared reflector in said first direction does not cause said PIR sensor to generate a signal indicative of motion of said person, panning said infrared reflector in a second direction away from said nominal pointing angle.

5. The device recited in claim 4, wherein said first direction is left and said second direction is right.

6. The device recited in claim 4, wherein if panning said infrared reflector in said first or second direction causes said PIR sensor to generate a signal indicative of motion of said person, said controller circuitry is operative to generate a signal indicating said space is occupied.

7. The device recited in claim 4, wherein if panning said infrared reflector in said first or second direction does not cause said PIR sensor to generate a signal indicative of motion of said person, said controller circuitry is operative to put said device in a standby state.

8. The device recited in claim 7, wherein said standby state comprises positioning said infrared reflector to said nominal pointing angle.

9. The device recited in claim 7, wherein said standby state has a predefined duration.

10. The device recited in claim 9, wherein said controller circuitry, at the expiration of said predefined duration, resumes selectively altering said pointing angle of said infrared reflector.

11. The device recited in claim 8, wherein said PIR sensor is operable to detect motion during said standby state.

12. The device recited in claim 1, wherein said PIR sensor comprises at least two pyroelectric infrared elements.

13. A method to detect occupancy of a space using a passive infrared (PIR) sensor having a fixed field of view, comprising the steps of: receiving, by a detector circuit, a signal from a PIR sensor indicative of motion of a person within a space; generating, by a control circuit, a signal to control an electromechanical device coupled to an infrared reflector positioned proximate to said PIR sensor for re-directing infrared radiation received from within said space toward said PIR sensor; and, selectively altering a pointing angle of said infrared reflector, using said electromechanical device, whereby the relative position of said person is shifted within said fixed field of view of said PIR sensor, thereby simulating motion of said person even when stationary.

14. The method recited in claim 13, wherein a nominal pointing angle of said infrared reflector is 45 degrees from the line normal to said PIR sensor.

15. The method recited in claim 13, wherein selectively altering said pointing angle of said infrared reflector comprises periodically panning said infrared reflector in a first direction away from a nominal pointing angle if motion of said person has not been detected for a predefined wait time.

16. The method recited in claim 15, wherein, if panning said infrared reflector in said first direction does not cause said PIR to generate a signal indicative of motion of said person, panning said infrared reflector in a second direction away from said nominal pointing angle.

17. The method recited in claim 16, wherein said first direction is left and said second direction is right.

18. The method recited in claim 16, wherein if panning said infrared reflector in said first or second direction causes said PIR to generate a signal indicative of motion of said person, said controller circuitry is further operative to generate a signal indicating said space is occupied.

19. The method recited in claim 16, wherein if panning said infrared reflector in said first or second direction does not cause said PIR to generate a signal indicative of motion of said person, said controller circuitry is operative to enter a standby state.

20. The method recited in claim 19, wherein said standby state comprises positioning said infrared reflector to said nominal pointing angle.

21. The method recited in claim 19, wherein said standby state has a predefined duration.

22. The method recited in claim 21, wherein said controller circuitry, at the expiration of said predefined duration, resumes selectively altering said pointing angle of said infrared reflector.

23. The method recited in claim 20, wherein said PIR sensor is operable to detect motion during said standby state.

24. A microcontroller for use with a passive infrared (PIR) sensor having a fixed field of view to detect occupancy of a space, said microcontroller comprising: detector circuitry operable to receive a signal from a PIR sensor indicative of motion of a person within a space; and, controller circuitry operable to generate a signal to control an electromechanical device coupled to an infrared reflector positioned proximate to said PIR sensor for re-directing infrared radiation received from within said space toward said PIR sensor, said controller circuitry operable to selectively alter a pointing angle of said infrared reflector, using said electromechanical device, whereby the relative position of said person is shifted within said fixed field of view of said PIR sensor, thereby simulating motion of said person even when stationary.

25. The microcontroller recited in claim 24, wherein said controller circuitry is operable to nominally adjust said pointing angle to be 45 degrees from the line normal to said PIR sensor.

26. The microcontroller recited in claim 24, wherein said controller circuitry is operable to periodically generate a signal to cause said infrared reflector to pan in a first direction away from a nominal pointing angle if motion of said person has not been detected for a predefined wait time.

27. The microcontroller recited in claim 26, wherein, if panning said infrared reflector in said first direction does not cause said PIR to generate a signal indicative of motion of said person, generating a signal to pan said infrared reflector in a second direction away from said nominal pointing angle.

28. The microcontroller recited in claim 27, wherein if panning said infrared reflector in said first or second direction causes said PIR to generate a signal indicative of motion of said person, said control circuitry is operative to generate a signal indicating said space is occupied.

29. The microcontroller recited in claim 27, wherein if panning said infrared reflector in said first or second direction does not cause said PIR to generate a signal indicative of motion of said person, said controller circuitry is operative to enter a standby state.

30. The microcontroller recited in claim 29, wherein said standby state comprises generating a signal to position said infrared reflector to said nominal pointing angle.

31. The microcontroller recited in claim 29, wherein said standby state has a predefined duration.

32. The microcontroller recited in claim 31, wherein said control circuitry resumes selectively altering said pointing angle at the expiration of said predefined duration.

33. The microcontroller recited in claim 31, wherein said detector circuitry is operable to receive and process a signal from a PIR sensor during said standby state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a more complete understanding of the disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings, in which:

[0014] FIG. 1 illustrates the general structure of a passive infrared (PIR) sensor;

[0015] FIG. 2 illustrates the operational characteristics of a PIR sensor;

[0016] FIG. 3 illustrates the challenge of using a PIR sensor for an occupancy detector;

[0017] FIG. 4 illustrates a device architecture for an occupancy detector utilizing a PIR sensor having a fixed field of view and a controllable-angle infrared reflector;

[0018] FIG. 5 illustrates example infrared reflections from a controllable-angle infrared reflector; and

[0019] FIG. 6 illustrates an example control scheme an occupancy detector.

DETAILED DESCRIPTION

[0020] FIG. 3 illustrates the challenge of using a PIR sensor for an occupancy detector. As noted supra, PIR sensors output a voltage dependent on the degree of infrared radiation they receive. They are commonly used for motion detection, since when a warm-bodied person 301 passes through the sensor's field of view the output voltage is disturbed beyond its baseline level (which otherwise drifts based on background radiation and other factors). When the person is not moving 302, however, there is no change in the received IR signal and it is difficult to distinguish the IR signal of the person from the baseline IR level of the monitored space.

[0021] For a PIR motion sensing device, a detector circuit 310 is coupled to, and receives a voltage signal from, the PIR sensor 100. The detector circuit 310 can be, for example, a discrete analog or an integrated digital implementation. In a typical discrete analog implementation, the PIR sensor 100 output is scaled and filtered through multiple op-amp stages within detector circuit 310; this helps to ensure a large enough signal amplitude and to focus the detection only on frequency ranges likely to correspond to human motion. The processed waveform then goes to a comparator stage which toggles a digital logic output to alert a system that voltage deviations have exceeded a configured sensitivity threshold and that motion had occurred within the monitored space. With the right component selection, standby currents can be below 2 uA. For an integrated digital implementation, the PIR sensor waveform can be acquired by an ADC input of a microcontroller, then digital signal processing algorithms are applied to filter for human motion and determine whether or not motion had occurred. Overall current consumption can still be kept low (e.g., <10 uA) with this approach since the low frequencies of motion signals allow for very low sample rates (e.g., 20 samples/sec). This allows the system to spend the vast majority of time (>99%) in a low-power sleep state. Some analog signal conditioning, however, may be required to interface to the PIR sensor 100. One example of a suitable microcontroller for an integrated digital implementation is Texas Instruments MSP430FR2355 MCU.

[0022] Turning now to FIG. 4, illustrated is an occupancy detection device architecture 400 for an occupancy detector utilizing a PIR sensor 100 having a fixed field of view and a controllable-angle infrared reflector 410. Rather than relying on the motion of the target, such as stationary person 302, to create an alternating infrared profile through the sensor's fixed field of view, the monitored space can be periodically swept by an infrared reflector 410, positioned proximate to the PIR sensor 100 for re-directing infrared radiation received from within the monitored space toward the PIR sensor. An electromechanical device 420, such as a micromotor, is coupled to the infrared reflector and operative to alter a pointing angle thereof in response to a control signal 431 from detector and controller circuitry 430; the detector and controller circuitry can be, for example, integrated together in a microcontroller, such as one from Texas Instruments' MSP430 family of microcontrollers; the highly integrated smart analog combo functions of MSP430 microcontrollers can be used for conditioning and processing of a signal 101 received from PIR sensor 100, as well as for control of the electromechanical device 420, via a signal 431, for altering the pointing angle of the infrared reflector 420; an example of a control scheme is described hereinafter with reference to FIG. 6. Altering the pointing angle of the infrared reflector 410 redirects infrared waves from the monitored space to the PIR sensor 100, shifting the view perceived the sensor left or right, which results in a received IR signal comparable to that of a moving target being received by a stationary sensor. Thus, the occupancy detection device architecture 400 relies on a single standard analog PIR sensor 100, rather than more complex electronics known in the art.

[0023] Referring now to FIG. 5, illustrated are example infrared reflections from a controllable-angle infrared reflector 410, as perceived by a PIR sensor 100 having a fixed field of view, as the pointing angle of the reflector is panned from left to right, causing a stationary person 501 to be perceived by the sensor as moving from right to left in the sequence of images 510, 520, 530 and 540, respectively. From the perspective of the PIR sensor 100, and associated detection circuitry, the relative position of the person 501 is shifted within the fixed field of view of the PIR sensor, thereby simulating motion of the person—even when stationary. The artificial movement of the person 501 as perceived by the PIR sensor (and associated detection circuitry) triggers a sensor response similar to that of a person walking perpendicular to a stationary sensor, as illustrated by signals 201 and 202 in FIG. 2.

[0024] Finally, referring to FIG. 6, illustrated is an example control scheme 600 (or “state diagram”) for an occupancy detector utilizing a PIR sensor 100 having a fixed field of view and a controllable-angle infrared reflector 410, as illustrated in FIG. 4; the control scheme can be implemented in, for example, detector and controller circuitry 430. The control scheme 600 is characterized by various states, and responses/actions causing the transition between states, dependent on the output signal from PIR sensor 100 and the pointing angle of infrared reflector 410.

[0025] Starting in state 610 (“standby state”), the PIR sensor 100 is active and any associated detector circuitry of detector and controller circuitry 430 is operational; this is a low-power state wherein preferably only the minimal amount of circuitry is enabled. In state 610, the infrared reflector 410 is also preferably positioned to a nominal pointing angle; for example, the nominal pointing angle of the infrared reflector 410 is set to be 45 degrees from the line normal to the PIR sensor 100.

[0026] While in the standby state 610, if motion of an object (i.e., a person) is detected 620, indicating the space is occupied, the controller moves to a state 620, which can be used to trigger, via a signal 621, an action 630, such as turning on lighting or adjusting an HVAC thermostat. Once the triggered action is completed, the control scheme returns to the standby state 610. If further motion of the person is detected, the control scheme again steps through state 620 and performs any programmed actions. If, however, no motion is detected for a predefined time (i.e., no signal is received from PIR sensor 100 indicative of motion of the person within the monitored space), it is possible that the previously-perceived person moved to a location within the space outside the field of view of the PIR sensor 100. Or it is possible that the person is still within the field of view of the PIR sensor 100 but is stationary—and, thus, not triggering a signal from the PIR sensor indicative of the person's continued presence. In either case, the control scheme 600, in the absence of a signal indicative of continued occupancy for a predefined wait time (t.sub.WAIT), generates a signal for the electromechanical device 420 to alter the pointing angle of the infrared reflector 410.

[0027] In the example control scheme 600, in the absence of a signal from the PIR sensor 100 indicative of continued occupancy for the predefined time (t.sub.WAIT), the infrared reflector is rotated to the right 640, thus shifting the field of view of the PIR sensor to the left by an angle φ.sub.L (as described supra with respect to FIG. 5). If motion is still not detected 642, the infrared reflector 410 is rotated to the left, shifting the field of view of the PIR sensor to the right by an angle φ.sub.R. In this example, φ.sub.L can be equal to φ.sub.R, which means the field of view of the PIR sensor would be panned by equal measures to the left and right, thus expanding the nominal field of view of PIR sensor 100. In addition to expanding the nominal field of view, panning the field of view in the absence of detected motion will alter the relative position of the person within the fixed field of view of the PIR sensor (if still occupying the room), thereby simulating motion of the person even when stationary.

[0028] The example control scheme 600 can be modified as desired to balance the time to confirm occupancy of a monitored space against increased power of the device. For example, the predefined wait time (t.sub.WAIT) can be lengthened, which will delay confirmation of continued occupancy, but will reduce device power consumption. Similarly, the selective altering of the pointing angle of the infrared reflector can be iteratively and/or progressively performed to the left, then the right, or alternately to the left and right by progressively greater angles, to fully sweep the monitored space. An increase in the frequency of altering the pointing angle of the infrared reflector 410, however, will increase the power demands of the controller circuitry of detector and controller circuitry 430 and the electromechanical device 420. Such concerns about power demands, however, are generally only relevant with respect to battery-powered occupancy detectors.

[0029] The technical principles disclosed herein provide a foundation for designing occupancy detection devices utilizing a single PIR sensor. The examples presented herein illustrate the application of the technical principles and are not intended to be exhaustive or to be limited to the specifically-disclosed circuit topologies or methods of operation; it is only intended that the scope of the technical principles be defined by the claims appended hereto, and their equivalents.