Re: Occupancy detection

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Bill Kearney" <wkearney-99@hot-mail-com> wrote in message
news:z7WdnRUYYaZFISTbnZ2dnUVZ_gmdnZ2d@xxxxxxxxxxxxxxxx
> > I don't want anyone to be able to press ALL LIGHTS OFF in one part of
the
> > house while a person is descending the stairs in another.
>
> But just how likely is that to happen?

All it takes is once to cause serious problems.  The "ALL OFF" scenario is
just once facet of the problem.  As you well know <g> the X-10 protocol is
vulnerable to a number of problems related to speed, collisions and the
one-way nature of the sensors.  What's more likely is that a command gets
dropped, stepped on or otherwise garbled and the light never comes on.  Non
permisso!  I want the stairway light to come on as soon as someone crosses
through the door frame and stay on until they are well off the stairs.  I
also want the light to respond to ALL OFF when safe to do so.

> That and any motion sensor would trip again on seeing motion and turn the
like back on.
> What's going to happen faster?

Sadly "any" doesn't apply to the Hawkeyes.  To maximize battery life they're
stingy on instant retries.  Try this test with a stopwatch.  See how many
steps you can cover when moving at a good clip (imagine a family member in
distress!) in two seconds.  Stairwells are mission-critical areas where an
error can cause a bad outcome up to and including death.  The Hawkeyes
certainly won't reset fast enough to prevent disaster although I imagine
hardwired, A/C powered detectors will since they don't have to worry about
conserving battery life.  I'd like the system to respond to X-10 commands,
but not be controlled by them.  It should also not respond to X-10 if that
would create a safety hazard.

> Controlling 'All Off' but keeping exceptions for currently
> detected motion cannot be accomplished at the device level.

I disagree.  It will take a number of components including X-10 Powerflash
and Universal modules as well as latchable relays and timers, but I think it
can be accomplished without adding a PC and all the unreliability that
entails.  If a small set of condition equals true, then accept the X-10
command, if not, ignore (or queue) the command until the proper conditions
exist (i.e. stairway empty).  Remember, the switch that controls the light
will not be an X-10 unit, but a hard-wired, relay controlled unit that
responds only to low voltage contact closures.  Those contact closures would
have X-10 commands as potential input, but would primarily respond to the
sensors determining someone had crossed the threshold of the stairway.

> It would require a computer (dedicated PC or whatever) and intercepting
the 'All Off'
> functions entirely.  This may be a bigger problem as the 'All off'
function
> is usually directly sent from controls to devices and can't be easily
> disregarded.  If keypads that had 'All off' functionality had the ability
to
> reprogram the housecode for just that key then it might work.  But none
> offer this, they only allow one housecode for all buttons, not
individually.

And that's precisely why you'd need the system I described - a hardwire
control of that particular light that can accept X-10 commands if the
conditions are right.  It's a question of downsides.  If the system
"guesses" wrong, the worst that SHOULD happen is that the light stays on and
I contribute more to global warming than I'd like.  Right now, the worst
that can happen is that the light goes out in mid-stride and someone loses
their footing as a result.  From a quick scan on Google I found that an
estimated 2.5 million injuries, and a further 4000 deaths in the UK in 1995
were due to home accidents. About 230,000 of these injuries and 497 deaths
resulted from falls on stairs.  I'd guess the numbers for the US are equal
or higher, per capita.

> You'd have to change the housecode and use a PC to intercept and
retransmit
> all keypresses, not just the 'All off'.  This adds an unacceptable delay
as
> the commands have to get sent twice.  They're already 'slow enough' from
the
> keypads directly to the devices.  Adding a PC into the loop will
definitely
> be a WAF problem.

I agree completely with all of that which is why I believe the stairway
lights cannot be connected directly to an X10 switch but need to connected
to a hardwired relay switch like the GE low voltage units.  The switch could
be then be connected to the X-10 network via a powerflash module or a PC
without inducing serious latency problems.

I'm looking to biology for design ideas.  When you touch something hot, you
pull away without really thinking about it.  Cognitive control, a la Gordon
Liddy willing himself to burn a hole in his arm, comes in at a different
level, overriding the local "reflex" response only after serious signal
processing occurs.

In this case, when an X-10 OFF command is received, all that happens is that
a latched relay line is activated.  No light gets turned off.  That only
happens if the sensor input determines that no one is on the stairs.  That's
the critical function here.  The system is designed with "Fail Safe"
principles in mind. (Raise your hand if you've seen either version of the
movie or read the book.) In this case, that means the light only gets shut
off if there's a certainty (more than two sensors "concur" - maybe even
three) that the stairs are unoccupied.  That's basically how grocery store
doors work.  They won't close unless the sonar, pressure mat and IR beam all
indicate no one in the way.  Still, little old ladies get knocked down all
the time so even that's not perfect.  If a single Hawkeye controlled the
average supermarket door, the courthouse would overflow with people who had
been batted by the door closing at the wrong time.  (-:

(!!!! [light bulb lights over my head]!!!!) One of the reasons I find these
discussions useful is that sometimes odd things click in just the right way.
Dave's comments about industrial controllers got me thinking about
commercial building stairwells and how they're set up.  Up until this minute
I didn't realize that part of my fail safe solution has to include
battery-powered emergency lamps of the type found in every high rise.  A
power failure on the stairs is a far more likely event than an errant ALL
LIGHTS OFF and I hadn't even thought of it until now. With a little
rewiring, I am sure I can interface my system to the emergency lights so
that if the 110VAC light did go out while the stairs were "loaded" then the
emergency lights would fire.  This would protect against a bulb popping as
you started down the stairs.

> I'd consider adding logic on a PC that tracked motion sensor status and IF
> an 'All off' was detected that signals be sent to immediately bring those
> lights back on.  But with a timer that monitored for any additional motion
> detection.  As in, the stairs sensed motion, an 'all off' was detected,
turn
> the stairs back on and wait X period of time to see if any other motion
was
> detected, if not, turn the stairs back off again.

That's a good idea but I'd feel a lot more sanguine about the system if the
premise was "don't turn off the lights for any reason unless the system is
certain the stairs are empty."  The scenario you suggest would certainly
work, but there are a lot of potential failure points.  Since I fell down
the stairs I have a better appreciation of why I wouldn't want to use a
crash-prone PC to keep me from crashing into the basement floor. (-:  I'm
going to try to find some wiring diagrams for commercial door closers to see
if they use a microcontroller or a simple circuit board with TTL components.

> I'm guessing it'd be far too much work trying to come up with a "fix" to a
> relatively unlikely or infrequent scenario.

Well, I agree.  If the cost in time, effort and materials is greater than
running a CFL 24x7 for 10 years, it's probably not worth doing.  But I
believe it's going to turn out to be something that I can hack together with
TTL components.  I'll have to work out the requirements precisely so I can
decide whether I should go simple TTL or more complex microcontroller or
just restore the manual 3 way switches to the circuit.  Since I've already
fallen, I don't want to fall again so as unlikely the scenario may seem, I
want to design a system that can accommodate all of the failure modes I can
identify.  In this message alone I've identified two more conditions:
building power failure and bulb burnout.

--
Bobby G.