Re: Occupation sensor that works with people sitting still?

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"mike" <ki4fyy@xxxxxxxxx> wrote in message
news:Yc9Ah.5906$V64.5451@xxxxxxxxxxxxxxx

<stuff snipped>

> I think the original post was for use in a bedroom -- most bedrooms only
> have one entrance. Even if there were 2, the "in-counts" could be "or'd"
> and the "out-counts" could be "or'd". To make it robust, the direction
> of travel would need 2 sensors and they could be set apart by maybe 3
> feet or so. This might not be practical unless the doorway led to a
> hallway. Use modulated IR light beams for the sensors and TV remote
> control IR receiver modules to avoid problems with extraneous lights.
> I've seen sensors in museums and restrooms that probably work like that
> to shut off the lights when nobody is present. My guess is that someone
> could do all this with a basic stamp and a handful of other parts.

And a small matter of programming.  (-: The devil is in the details.
Someone carrying a laundry basket in front of them through a narrow doorway
is likely to register twice with only a beam interruption sensor.  It's not
a bad idea, but it's clearly got to be just a piece of the "is this room
occupied" puzzle.

Automatic door failures have generated a lot of litigation, mainly because
so many early models knocked over the frail and elderly, who often moved too
slowly to be detected by single sensors.   Look at any large grocery store's
automatic doors (they're the primary defendants in such suits) and you'll
see they'll have at least two (and often four) different types of occupancy
sensors controlling their doors.  One type of sensor simply isn't good
enough (or failure-proof enough) to do the job reliably.

Pressure mats, light beams, PIRs and ultrasonic or microwave transducers are
the ones I've seen most often in commercial establishments.  They are
designed to operate in an interlocking fashion and prevent the door from
opening *into* a person for any reason.   Stores that have vestibules (two
sets of doors and a open area between them) are particular problems because
people often pile up there inclement weather waiting for rides and so don't
fit the designers expectations of orderly exit and entry by people walking
at a normal pace.

It took knocking a lot of little old ladies over, but today's automatic door
systems are quite highly evolved compared to the first generation of doors.
There are probably an equal number of crushed children and dented dogs that
have contributed to advances in garage door safety in much the same way as
all those grannies.   )-:

--
Bobby G.