Abstract: A passive low power device for detection of boundary crossings includes a dual element pyro-electric infrared (PIR) sensor. The sensor is designed with a lens that provides a very narrow field of view and two pyro-electric elements that produce a waveform with two voltage swings of opposite polarity when a warm object moves past the sensor. The waveform is filtered and amplified before it is passed on to a comparator. The comparator triggers off the extremes of each waveform. The comparator includes two outputs that are normally high, but go low when a change in infrared radiation is detected. A processor makes an approximation of the zero crossing time based on the rising edge of the first comparator output. This approximate zero crossing time serves as an estimate of the boundary crossing time.

Abstract: A passive low power device for detection of boundary crossings includes a dual element pyro-electric infrared (PIR) sensor. The sensor is designed with a lens that provides a very narrow field of view and two pyro-electric elements that produce a waveform with two voltage swings of opposite polarity when a warm object moves past the sensor. The waveform is filtered and amplified before it is passed on to a comparator. The comparator triggers off the extremes of each waveform. The comparator includes two outputs that are normally high, but go low when a change in infrared radiation is detected. A processor makes an approximation of the zero crossing time based on the rising edge of the first comparator output. This approximate zero crossing time serves as an estimate of the boundary crossing time.