Low power, inexpensive velocity detection using a pir array

Abstract

Methods and systems may include a system including a first passive motion sensor having a lateral field of view with a first edge and a second passive motion sensor having a lateral field of view with a second edge that is substantially parallel to the first edge. The first and second edges can define a virtual beam. The system may also include logic to receive signals from the first and second passive motion sensors and determine a gait velocity and level of activity based on the signals from the first and second passive motion sensors.

1 . A method comprising:
 partitioning an area into a plurality of zones using a plurality of virtual beams, the plurality of virtual beams being defined by edges of lateral fields of view of a plurality of passive motion sensors; and   determining a gait velocity of a subject based on the subject's movement through the plurality of zones as measured by signals from the plurality of passive motion sensors.   
     
     
         2 . The method of  claim 1 , further comprising determining a level of activity of the subject in one of the plurality of zones based on a time spent by the subject in the zone as measured by signals from the plurality of passive motion sensors. 
     
     
         3 . The method of  claim 1 , wherein determining the gait velocity of the subject comprises obtaining a time of entry into and a time of exit from one of the plurality of zones of the subject based on an edge transition of a signal from the plurality of passive motion sensors. 
     
     
         4 . The method of  claim 1 , wherein the passive motion sensors comprise passive infrared sensors. 
     
     
         5 . The method of  claim 1 , further comprising retrieving one or more distances between virtual beam edges from a memory location. 
     
     
         6 . The method of  claim 1 , wherein the plurality of passive motion sensors comprises a first passive motion sensor and a second passive motion sensor disposed substantially parallel to the first passive motion sensor. 
     
     
         7 . The method of  claim 1 , wherein the plurality of passive motion sensors is disposed such that an expected motion to be detected is in a direction substantially perpendicular to the virtual beams. 
     
     
         8 . An apparatus comprising:
 a plurality of passive motion sensors, each of the passive motion sensors having a lateral field of view with an edge, the edges defining a plurality of virtual beams that partition an area into a plurality of zones,   wherein output signals from the passive motion sensors indicate one or more of an order of activation of the passive motion sensors, a time difference between activation of the passive motion sensors, and a distance between virtual beam edges.   
     
     
         9 . The apparatus of  claim 8 , wherein the plurality of passive motion sensors comprises two passive motion sensors disposed horizontal to one another and define a two-dimensional vertical beam such that, if the two passive motion sensors are mounted to a wall of a hallway, the two-dimensional vertical beam is substantially perpendicular to a longitudinal axis of the hallway. 
     
     
         10 . The apparatus of  claim 8 , further including one or more leveling indicators. 
     
     
         11 . The apparatus of  claim 8 , wherein the plurality of passive motion sensors is disposed such that an expected motion to be detected is in a direction substantially perpendicular to the virtual beams. 
     
     
         12 . The apparatus of  claim 8 , wherein the plurality of passive motion sensors comprises a first passive motion sensor and a second passive motion sensor disposed substantially parallel to the first passive motion sensor. 
     
     
         13 . A system comprising:
 a plurality of passive motion sensors, wherein each of the passive motion sensors has a lateral field of view with an edge, the edges defining a plurality of virtual beams that partition an area into a plurality of zones; and   a processor, in communication with a memory, configured to:
 receive signals from the plurality of passive motion sensors, and 
 determine a gait velocity of a subject based on the subject's movement through the plurality of zones as measured by signals from the plurality of passive motion sensors. 
   
     
     
         14 . The system of  claim 13  wherein output signals from the passive motion sensors indicate one or more of an order of activation of the passive motion sensors, a time difference between activation of the passive motion sensors, and a distance between virtual beam edges. 
     
     
         15 . The system of  claim 13 , wherein the processor is further configured to determine a level of activity of the subject in one of the plurality of zones based on a time spent by the subject in the zone as measured by signals from the plurality of passive motion sensors. 
     
     
         16 . The system of  claim 13 , wherein determining the gait velocity of the subject comprises obtaining a time of entry into and a time of exit from one of the plurality of zones of the subject based on an edge transition of a signal from the plurality of passive motion sensors. 
     
     
         17 . The system of  claim 13 , wherein the memory is configured to store one or more distances between virtual beam edges. 
     
     
         18 . The system of  claim 13 , further comprising a leveling indicator. 
     
     
         19 . The system of  claim 13 , wherein the plurality of passive motion sensors comprises two passive motion sensors disposed horizontal to one another and define a two-dimensional vertical beam such that, if the two passive motion sensors are mounted to a wall of a hallway, the two-dimensional vertical beam is substantially perpendicular to a longitudinal axis of the hallway. 
     
     
         20 . The system of  claim 13 , wherein the passive motion sensors comprise passive infrared sensors.