Abstract:
A method of sensing motion in a predetermined area is provided. The method may include using a digital output motion sensor to produce a digital output signal indicative of the presence of motion in the predetermined area. The method may further include transmitting the digital output signal along a signal path independent of analog amplification and filtering. The method may also include using a microprocessor coupled to the signal path to receive the digital output signal and to process the digital output signal.

Description:
This application is a continuation application of U.S. application Ser. No. 11/970,017, filed Jan. 7, 2008, now U.S. Pat. No. 7,924,155. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to lighting, and other load, controls. More specifically, this invention relates to lighting, and other load, controls that work in conjunction with an occupancy sensor. Even more specifically, this invention relates to passive infrared (“PIR”) occupancy sensors utilizing a pyroelectric sensor. 
     A PIR sensor is an electronic device which measures infrared light radiating from objects in its predetermined area and/or field of view. PIRs detect motion when an infrared source with one temperature, such as a human, passes in front of an infrared source with another temperature, such as a wall. 
     Existing PIR occupancy sensors utilize a pyroelectric sensor that has an analog voltage output. This output is amplified and filtered using a high gain operational amplifier in order to interface with conventional logic and/or microcontrollers. 
     The high gain used in conventional PIR sensors has the disadvantages of increasing noise in the signal path. Noise sources in the signal path include signal noise, thermal noise, power supply noise, transients from the AC main supply lines, and switching noise from a relay or TRIode for Alternating Current (“Triac”) (a bidirectional electronic switch that can conduct current in either direction when it is triggered), as well as radiated noise from the environment. 
     Another source of noise [from the point of view of the sensor signal] is radiated signals from an [wireless] RF communication means such as a Blackberry™ device or other similar device. A high gain amplifier is likely to pick up these transmissions, along with additional power supply noise generated by the current pulses from the transmission. This kind of noise is difficult to filter out using analog filtering. In fact, for some signals it may be that the transmission cannot be filtered out. 
     It would be desirable to eliminate the high gain amplifier from the signal path of the PIR at least for the purpose of mitigating the amplification of the noise associated with the RF transmission as well as the power supply noise. 
     SUMMARY OF THE INVENTION 
     A passive infrared-based occupancy sensor load control including a digital output motion sensor that produces a digital output signal and transmits the digital output signal along a signal path independent of analog amplification and filtering is provided. The digital output signal can indicate the presence or absence of motion. The load control can also include a microprocessor coupled to the signal path. The microprocessor may receive and process the digital output signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the purposes of illustrating the various aspects of the invention, there are shown in the drawings forms that are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
         FIG. 1  is a schematic diagram of a prior art circuit typically used with an analog output passive infrared output sensor. 
         FIG. 2  is a schematic diagram of a basic circuit for a digital sensor according to the invention. 
         FIG. 3  is a schematic diagram of a preferred embodiment of a circuit according to the invention. 
         FIG. 4  is an illustrative flow diagram of a preferred embodiment of a method according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Using a digital output pyroelectric sensor may allow for the elimination of the analog amplification and filtering, which will improve the signal to noise ratio and make the product less susceptible to periodic and or transient noise. Such digital pyroelectric sensors are commercially available, for example, as the DigiPyro™ family parts PYD1978, PYD 1988 manufactured by Perkin Elmer, Inc., of Waltham, Mass. 
     As described above with respect to the analog output pyroelectric sensor, the large gain amplifier and filter introduce significant noise into the signal. It follows that by using the large gain amplifier and filter, existing sensors lose information about noise in the PIR signal prior to amplification and filtering. The pyroelectric sensor responds to thermal energy in the environment as well as thermal energy from people. The filters found in existing sensors generally have a lowpass filter of around 1 second, and a large time constant. The term “one second” to describe the filter is used for the following reason. Usually human motion frequencies are in the range of 0.1-1 Hz. The filters are typically designed around this frequency and the filter attenuates DC components, which typically depend on temperature and vary greatly with the manufacturing processes, and higher frequencies which are generated not by human body motion but by other existing noise factors. Accordingly, the sensor looks at the change in the signal and not the signal itself. As such, any frequency information about the signal below this cutoff is lost. The frequency information that is lost is typically outside the frequency band of from about 0.25-1 Hz to from about 10-15 Hz or other suitable frequencies. 
     The digital signal path occupancy sensor, on the other hand, can have access to the noise information related to the PIR signal as well as to frequency information that otherwise would have been filtered out by the lowpass filter. 
     It should be noted that the systems and methods described in this patent application may apply to manual-ON sensors (vacancy sensors) and/or automatic-ON sensors (occupancy sensors). A manual-ON sensor (vacancy sensors) is a lighting system that is turned ON manually and shuts OFF in response to a predetermined period of vacancy as determined by a sensor. An automatic-ON sensor (occupancy sensors) is a lighting system that is turned ON in response to a signal from a sensor that corresponds to the presence of a heat-source, such as a human, in a predetermined area and/or field of view. 
     Additionally, load controls using systems according to the invention can also be implemented. Such load controls may include turning the load ON or OFF and/or dimming the load as needed. Such load control may be achieved, in certain embodiments, using either a relay or a thyristor—e.g., the triac described above. In certain embodiments of the invention the load controls may be implemented to control only a light or a lighting device to the exclusion of controlling other devices such as controlling a security system using the motion sensor according to the invention. In other embodiments, the load control may be implemented to control various loads such as fans, heating, vacuum and air conditioning systems (“HVAC”), security systems, electronically operable window shades and/or any other suitable electronic loads. 
     A PIR based occupancy sensor load control according to the invention preferably includes an embodiment wherein the PIR signal is processed only digitally. This processing preferably occurs independently of analog amplification and filtering. In certain embodiments of the invention, a range and/or sensitivity adjustment can be implemented via digital signal processing. 
     In some embodiments of the invention, adapting algorithms that act on the raw digital signal may be implemented. The PIR based occupancy sensor load control may also act to control a load using a relay as the load control. In an alternative embodiment of the invention, the load control may be a dimmer. 
     A PIR based occupancy sensor load control according to the invention may also include a visible indicator of a soon to expire time-out of the load. In the case where a light is the load, such a visible indicator may be adapted to produce some sequence of dimming and brightening the controlled light to warn the occupant that lights will turn OFF soon. The visible indicator may also include a brightness level display that is used to indicate duration of a delayed-off time period. The brightness level display may also be used to indicate the dim level of the light. 
     An alternative embodiment of the invention may include a PIR occupancy sensor lighting control that displays the level of ambient light measured on an LED display. Such a PIR occupancy sensor lighting control may include a programming mode, wherein user adjustments including but not limited to sensitivity adjustments are programmed digitally. One embodiment of such a programming mode may be entered by pressing and holding the ON/OFF button for a predetermined period of time. Another embodiment of such a programming mode may be entered by pressing the ON/OFF button and the bright button substantially simultaneously for a predetermined period of time. 
       FIG. 1  shows a conventional passive infrared occupancy sensor circuit  100  that utilizes a pyroelectric sensor  102  that has an analog voltage output  104 . Circuit  100  also typically includes comparator  106  which provides an output that indicates whether motion has been detected. 
     Circuit  100  also typically includes an operational amplifier  108  to amplify the signal corresponding to the output from sensor  102 . In such a circuit, VCC is 5V and the signal corresponding to the output from sensor  102  is referenced to ½ VCC (via a resistor divider that includes resistors  110  and  112 .) Other resistors  114 ,  116 ,  118 ,  120 ,  122 ,  124 , and  126  as well as capacitors  128 ,  130 ,  132 ,  134 ,  136 ,  138  and  140  may be present for conditioning the signal corresponding to the output from sensor  102  in order to adapt the signal for use by microprocessor  140 . Microprocessor  140  preferably controls an LED/Display  142  associated with a load control (not shown) as well as the load itself, which is shown as the load_control line  144 . 
     In circuit  100 , when motion is present, an output signal level can indicate that motion is present by varying both positively and negatively around the reference. 
     It is known in existing PIR sensors to utilize adapting algorithms that obtain characteristics of the signal post-amplification—i.e., when the signal is output from opamp  108 —and compare historic information with the obtained characteristics to adjust the sensitivity and/or the delayed-off time of a sensor. The delayed-off timer of a sensor may send an instruction as to how much time a load should remain ON when a no-motion condition is detected. Certain characteristics that may be obtained for use by the adapting algorithms include a characteristic that reflects the frequency of pulses received from sensor  102 , or a characteristic that reflects a correlation between amplitude and frequency of pulses. In addition, these characteristics may be used to help improve performance—e.g., to keep a light ON when someone is in the room, and turn the light OFF as soon as possible when no one is in the room. 
     Whereas conventional PIR circuits use microprocessors to process signals from sensors only after the signals have been substantially conditioned—e.g., amplified and/or filtered—the circuits according to the invention, on the other hand, are adapted to receive the signals directly from the motion sensor. Accordingly, circuits according to the invention preferably process raw signals from the sensor substantially independent of any further signal conditioning. Using a preferably substantially entirely digital signal path allows for the creation of digital signal processing algorithms that characterize the PIR signal on the scale of milliseconds, thus improving the reaction of the algorithms by more than an order of magnitude over conventional passive IR sensors. 
       FIG. 2  shows a basic circuit  200  for a digital sensor having a digital signal path according to the invention. Circuit  200  includes microprocessor  202 , digital output sensor  204 , load_control  206 , and LED/Display  208 . A practical implementation of circuit  200  may include a bypass capacitor (not shown) or other filtering components for stabilizing the VCC connection. 
     In certain embodiments of the invention, motion may be detected by sensor  204 . In response to the detection of motion, sensor  204  may provide an output signal to microprocessor  202 . It can be seen from  FIG. 2  that sensor  204  may be implemented independently of any additional signal conditioning components. Instead, the output signal of sensor  204  may be directly fed into microprocessor  202 . In response to such an output signal, microprocessor  202  can control load_control  206  and LED/Display  208 . Alternatively, sensor  204  may be implemented with only a minimum of additional signal conditioning components. 
       FIG. 3  shows a preferred embodiment of a circuit  300  according to the invention. Circuit  300  preferably includes a microprocessor  302 , sensor  304 , load_control  303 , and LED/Display  305 —similar to the elements of circuit  200  shown in  FIG. 2 .  FIG. 3  also shows various other modules which are controlled by, or provide signals to, microprocessor  302 . These modules include photocell module  306 . The photocell module allows the sensor to be set to turn light ON only when it is dark in the room or a certain light level is present in the room. These modules also include bright/dim buttons  308  which allow a user to manually adjust light level in case of a dimming sensor, zero crossing detection circuit  310  that may be necessary for dimmer control or to synchronize switching with zero crossing, indication module  312  that displays relative light level preferably with an LED bar, connector with the power supply board  314 , wired communication line transmitter (YW Transmitter)  316 , occupancy display signal  318 , optical serial communication port  320 , wired communication line receiver  322 , switch control signal  324 , and microcontroller reset pin  326 . 
     Algorithms according to the invention improve the distinction between thermal energy from the environment and thermal energy from a human, and allow for filters that may adaptively change depending on the signal conditions. 
       FIG. 4  shows a flow diagram of an exemplary algorithm  400  according to the invention. The algorithm may initiate by reading (or otherwise receiving) digital PIR sensor output, as shown in step  402 . Thereafter, for the purposes of use by the algorithm, the acquired value may be passed through a bypass second order (or higher) digital filter with approximate exemplary cutoff frequencies of about 1 Hz and about 10 Hz, as shown in step  404 . Alternatively, in other implementations of circuits according to the invention, the cutoff frequencies may be between about 0.25-1 Hz to about 10-15 Hz, or any other suitable set of cutoff frequencies as required for the algorithm. It should be noted that, as described above, the circuits according to the invention can recover information outside the frequency cutoff bands, nevertheless, for the purpose of the algorithm, the information outside the cutoff bands may not be necessary. 
     Following the filtering, a number of steps may be implemented. Step  406  shows comparing the conditioned—i.e., filtered—signal with a decision threshold. The decision threshold can be set manually or calculated based on the received signal&#39;s parameters. 
     Step  412  shows that the acquired signal may also be passed through a low pass filter to select a DC component of the signal. Thereafter, (or, alternatively, following step  404 ) the conditioned—i.e., filtered as shown in either step  404  or step  412 —signal may be passed through a low pass filter to analyze the trend (time constants for rising and falling values can be different) to use in calculation for an adaptive threshold. Step  416  shows calculating the adaptive threshold based on signal conditions such as, for example, light state (ON or OFF), time since switching light ON or OFF and occupancy signal frequency. Step  418  shows reading manual controls (settings and options), including include photo cell(s), temperature indicators, and other sensors. 
     Step  406  shows comparing the conditioned signal as conditioned in step  404  with the threshold formulated in step  416 . Step  408  shows generating a control signal for a switch or Triac to control the light at least in part in response to the comparison formed in step  406 . Step  410  shows an optional step of communicating information such as, for example, the information relating to the threshold, with other sensors and/or lighting controls. 
     Conventional sensors generally have a range [sensitivity] control to adjust how well the device detects motion. This adjustment affects either the amplifier gain, by the use of a potentiometer in the amplifier feedback path, or this adjustment affects the threshold of a comparator, again, by the use of a potentiometer. 
     Changing the amplifier gain has the consequence of affecting the signal and noise together, as well as adding additional electrical noise from the potentiometer. Changing the threshold of the comparator has the similar disadvantage of not discriminating between signal and noise. 
     Both methods—i.e., adjusting the amplifier gain and/or adjusting the threshold of the comparator—do not have the advantage of using the raw signal frequency information. By using the digital signal processing algorithms mentioned above it is possible to eliminate the need for this range control. Or, in an alternative embodiment of the invention, there can be a user control for altering the signal processing parameters. 
     In one additional exemplary embodiment of the invention, the microcontroller can implement different coefficients or cutoff frequencies for the digital filters described in steps  404  and/or  416 . Such different coefficients and/or different cutoff frequencies may result in improved control by affecting the signal and not the noise. 
     Occupancy sensors also typically have a time delay, and, for automatic-ON models, an ambient light level adjustment. Adjustments to the time delay and the ambient light level can generally be controlled via the microprocessor. 
     However, in conventional sensors, such adjustments typically require additional hardware to establish microprocessor control. The digital signal path according to the invention, on the other hand, eliminates the need for additional hardware because the adjustments can be implemented in the microprocessor, independent of additional analog hardware. 
     Yet a further embodiment of the invention deals with setting the various adjustments described above from a “programming mode” of the load control product. It is common for many load control products to have a ‘programming mode’, which allows the user to set certain parameters. However, for existing PIR sensors, it is not common to have a programming mode wherein the user can adjust the major settings because these settings are typically part of the analog circuitry. With the digital signal path according to the invention, it is possible for all settings to be performed as part of a ‘programming mode’. 
     Thus, systems and methods for providing digital occupancy sensor load controls have been described. 
     Aspects of the invention have been described in terms of illustrative embodiments thereof. A person having ordinary skill in the art will appreciate that numerous additional embodiments, modifications, and variations may exist that remain within the scope and spirit of the appended claims. For example, one of ordinary skill in the art will appreciate that the steps illustrated in the figures may be performed in other than the recited order and that one or more steps illustrated may be optional. 
     The methods and systems of the above-referenced embodiments may also include other additional elements, steps, computer-executable instructions, or computer-readable data structures. In this regard, other embodiments are disclosed herein as well that can be partially or wholly implemented on a computer-readable medium, for example, by storing computer-executable instructions or modules or by utilizing computer-readable data structures.