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[From a NA href="news://comp.home.automation/">comp.home.automation thread]
> You know, I've opened up a Hawkeye. The motion and light detectors are
> VERY small, less than 1/8" in diameter. Couldn't you do something like
> pinhole the circuit board onto the back of a picture?
Yeah, but it really wouldn't do what you want it to do.
If you check out most PIR sensors, you'll discover the circuit is set up
to trigger when there are sudden "jumps" in sensed heat levels. However,
you'll also discover that the PIR sensor is sensitive in a cone extending
out from the sensing area.
You turn "movement" into "jumps" with the facetted lense, which
causes people moving across the field of vision of the device to snap into
and out of focus as they leave the focus of one factt and into the focus
of the next. Remove that lense, and movement will remain in constant
focus... no jumps, no detection. (This, BTW, is why PIR sensors are almost
always "motion" sensors, not "presence" sensors.)
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