Re: Occupation sensor that works with people sitting still?

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Bill Kearney" <wkearney-99@hot-mail-com> wrote in message
news:nL2dnYWFH8XIfFDYnZ2dnUVZ_o-knZ2d@xxxxxxxxxxxxxxxx
> > I am searching for an occupation sensor to control lighting that can
> > sense occupation even if the person is remaining still (watching TV in
> > bed, sitting behind a computer).
> > Are there any solutions for this application?
>
> Much like the Holy Grail, people have been seeking for this for ages.
> There's no one good way to detect occupancy.

I think the solution is going to be very much like our own multiple senses
guide us to make decisions.  A combination of PIRs, threshold detectors in
doorways, sound detectors, vibration sensors and others, wired into a fairly
sophisticated decision-making computer could do a reasonable job of
assessing "occupancy."

The problem really is that any one sensor can get tricked pretty easily.  No
motion?  A PIR will report an empty room.  Two people walking out of a room
through a large doorway side-by-side?  That could fool an infrared beam
detector at the threshold that counts exits and entries.  The remarkable
software that's finding its way into consumer cameras to detect faces and
correct red-eye means it's not unreasonable to think tomorrow's occupancy
sensor would be smart enough to know when people's eyes are trained on a TV.

> Most sensor systems are setup so they only detect changes over a short
> period of time.  Otherwise you'd have to reset the things any time you
moved
> furniture.  Even something simple like moving an ottoman from one place to
> another would require resetting the baseline profile.  So you can imagine
> that being less than ideal.

I've wanted a simple sensor to fit under chair legs that detects and reports
weight changes.  Someone sits down?  Send a signal that indicates a high
level of probability that the user is still in the room, even if he doesn't
move.  If the occupant doesn't move for three days, call the coroner!  I'll
bet I could make something out of a old Hawkeye, some casters and some sort
of piezo-electric strain gauge.  Plenty of space under or behind most chairs
and couches to velcro a Hawkeye and lead some wires down to the chair leg.

> What's necessary is a combination of signals.  There's nothing currently
on
> the market that bundles it all up into a single "solution".

Precisely.  There was a very interesting occupancy sensor described here a
while back that used radio waves.  It set up a "known pattern" with two
antennas at opposite sides of the room (IIRC) and when that RF field was
disturbed by humans beings interposed between them.  Nearly 100 years ago
Naval Research Laboratory engineers in DC saw that a ship passing between a
transmitter and receiver on the Potomac river reflected a portion of the
waves back to the transmitter.

Since radar's proved so useful in "sky and sea" occupancy detection <grin>
it may have similar promise (albeit with much *lower* power transmitters)
for home occupancy sensors.  I know that my wireless 2.4GHz camera is very
adept at sensing when I am between transmitter and receiver.  The image
breaks up something fierce!

> Our new TV has an idle sensor.  If it hasn't seen an IR commands over an
> extended period it pops up a message indicating automatic shut off.  If
> we've fallen asleep and don't see the message it automatically turns
itself
> off.

I've got a similar set and any number of conditions are evaluated in the
decision to turn it off.  There's progress being made, it's just very slow
and uncoordinated.

> I worked in an office that at 10pm would blink the lights twice.  If
> you were still in the office and wanted the lights to remain on you had to
> manually toggle the wall switch.  Otherwise it'd automatically shut them
> off.

That's a good plan.  In the two places I use X-10 Hawkeyes it would be nice
if they could start just ramping the controlled lamp off slowly instead of
plunging the room into sudden darkness.  Hey, I could even do that via
programming.  Good idea, dude!

> Passively detecting occupancy is a very hard problem.  Tying it to
detected
> activity is a lot easier, but certainly not 'simple'.

It's why we have ears, eyes, noses, nerve endings, etc.  One sensor is too
easy to fool.  I remember back in sensory psych class learning about
microsaccades.  There are tiny movements the eye constantly makes because an
image falling on the retina fades quickly.  If you can truly immobilize the
eye and stop the any saccadic motion, the image you see turns very quickly
to gray.    Without microsaccades, staring intently at an object would cause
the image to vanish after a few seconds.  Rods and cones respond only to net
changes in brightness.  PIRs behave in a similar fashion.  As long as there
is motion, there's detection.  Maybe oscillating the PIR sensor is the
solution! (-:

http://en.wikipedia.org/wiki/Saccade

FWIW, you were probably right about the old refrigerator.  It sure does suck
down the kilowatts.  I should have a 7 day figure shortly.  The day to day
variations were just too great to extrapolate from.  As my wife pointed out,
I have to factor in the cost of all the frozen stuff we buy on sale that we
wouldn't have room for if we didn't have the second box.  These efficiency
calculations become very complex once you really begin to consider all the
parameters.

I'm not too worried yet.  As Dan pointed out, I am recapturing a lot of that
energy as heat and with subfreezing temps, that's a deal I can live with.
The summer time might present a different picture and I've been seriously
considering shutting it down during the months where electric prices rise
sharply.  That will solve the freeze up problem, too, since it's a lot
easier to flush and clean the unit when empty.  The final decision will rest
on how much dehumidification it provides as compared to the floor unit I
have.  I guess I can determine that by pints of water removed at X relative
humidity for each unit when the other's powered down.

--
Bobby G.