PIR motion detector circuitry with enhanced false-activation protection
Outdoor passive infra-red motion detector circuitry with circuit improvements that greatly reduce incidents of false activation. The motion detector includes one or more infra-red sensors and circuitry for amplifying and filtering the signal from the sensors. The amplification and filtering circuitry has a pass band for signals from the one or more sensors corresponding to a range of speeds of motion of a person moving in the field of view of the motion detector. The ability of the motion detector circuitry to filter out certain environmental sources of false activations is enhanced by providing the pass band with a very steep rolloff at the lower cutoff. In one embodiment the amplification and filtering circuitry is provided with three op amp stages, each stage being configured to contribute a nominal 6 db per octave rolloff to the lower cutoff. The amplification and filtering circuitry is also configured to provide the lower cutoff of the pass band with a fourth-order rolloff, which provides greatly enhanced protection against false activations from signals below the cutoff.
1. PIR motion detector circuitry for use in monitoring a field of view, said circuitry having one or more infra-red sensors and having amplification and filtering circuitry coupled to said one or more sensors, said amplification and filtering circuitry having a pass band for signals from said one or more sensors corresponding to a range of speeds of motion of a person in said field of view, wherein the improvement is characterized in that:
said pass band has a lower cutoff with a fourth-order rolloff providing substantial steepness for reducing false activations of said motion detector from signals below said lower cutoff.
2. PIR motion detector circuitry having one or more infra-red sensors and having amplification and filtering circuitry coupled to said one or more sensors, said amplification and filtering circuitry having a pass band for signals from said one or more sensors corresponding to a range of speeds of motion of a person across said one or more sensors, wherein the improvement is characterized in that:
said amplification and filtering circuitry has three op amp stages, each stage contributing a nominal 6 db per octave rolloff to the lower cutoff of said pass band.
3. The apparatus of claim 2 wherein each said op amp stage includes an input high-pass RC filter providing said rolloff.
4. The apparatus of claim 2 wherein said motion detector circuitry further comprises comparator circuitry defining a threshold, said comparator circuitry passing signals from said amplification and filtering circuitry exceeding said threshold, and the improvement is further characterized in that:
the output of the final stage of said amplification and filtering circuitry is coupled to said comparator circuitry through an RC filter network operative to pass signals above a low-frequency cutoff to ground and to pass signals below said low-frequency cutoff to said comparator circuitry for adjusting said threshold.
5. The apparatus of claim 4 wherein said comparator circuitry defines a window comparator having a center node establishing a center window value and wherein said RC filter network comprises at least one capacitor to ground and at least one resistive element connecting said final stage output to said center node for adjusting the window thresholds.
6. The apparatus of claim 4 wherein each said op amp stage includes an input high-pass RC filter providing said rolloff.
7. A method of reducing false activations in an outdoor PIR motion detector for monitoring a field of view, said motion detector having one or more infra-red sensors and having amplification and filtering circuitry coupled to said one or more sensors, said amplification and filtering circuitry having a pass band for signals from said one or more sensors corresponding to a range of speeds of motion of a person in said field of view, said pass band having a lower cutoff corresponding to a slowest speed of said person for triggering the motion detector, said method comprising:
providing said lower cutoff with a fourth-order rolloff.
8. A method of reducing false activations in an outdoor PIR motion detector for monitoring a field of view, said motion detector having one or more infra-red sensors and having amplification and filtering circuitry coupled to said one or more sensors, said amplification and filtering circuitry having a pass band for signals from said one or more sensors corresponding to a range of speeds of motion of a person in said field of view, said pass band having a lower cutoff corresponding to a slowest speed of said person for triggering the motion detector, said method comprising:
providing said amplification and filtering circuitry with three op amp stages, each stage being configured to contribute a nominal 6 db per octave rolloff to said lower cutoff.