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Re: Occupancy Sensors and No Light Switches


  • To: ukha_d@xxxxxxx
  • Subject: Re: Occupancy Sensors and No Light Switches
  • From: "paul gordon" <paul_gordon@xxxxxxx>
  • Date: Fri, 23 Jun 2000 11:34:21 GMT
  • Delivered-to: rich@xxxxxxx
  • Delivered-to: mailing list ukha_d@xxxxxxx
  • Mailing-list: list ukha_d@xxxxxxx; contact ukha_d-owner@xxxxxxx
  • Reply-to: ukha_d@xxxxxxx

I don't think this can really be done properly with only one form of input
(IE PIR's) - at least not economically!

I think you need a minimum of two types of sensor - PIR for movement
detection within the room, AND perimeter sensing to detect actual
entry/exit
into the room.

Perimeter detection could be by pressure pads by the doors - you'd need a
minimum of two of them - one outside the door, one inside, to be sure of
correctly deducing the direction of travel. This still would need care to
ensure you could guarantee detecting someone using the door - IE the pads
would need to be big enough to ensure that they would not be stepped over
by
accident... Also, some logic would be required to ensure that it didn't get
confused when only ONE pad is activated (someone walking around one one
side
of the door, without actually passing through it...)

Alternatively, a break-beam type detector in the door frame, positioned on
the "outside" of the door - IE the opposite side to which it
opens - so that
the door itself never breaks the beam regardless of whether its open or
closed...  This could be high enough of the ground to avoid pets, but still
always "see" people passing through.

A combination of both of these types of detector would probably be most
reliable - allied with some reasonably simple "state" tracking -
IE start
off knowing the room is empty, then using the detectors combined inputs,
it's possible to keep a counter of exactly how many occupants are in each
room at any time.

Entry or exit is determined by the order in which the zones are tripped,
and
the delay between each zone. - Of course, it's ALWAYS going to be possible
to fool any of these systems, but only if you're in the habit of
long-jumping through the doors in your house!!

A front door is a far more tricky proposition - what about when someone
comes to the door, and you have a conversation with them - both the inside
and outside pressure pads would be tripped concurrently (although not
simultaneously), and a break-beam would not be tripped at all! - anyone
care
to think about how you'd program for this scenario??

No doubt about it though - this is going to need a lot of zones!! - a
minimum of two per door, for every door in a room!...

Why can't it be as easy as it is on Star Trek?? - Any of those i-button
gizmo's have anything to offer for occupancy detection?? - How about
proximity detection within a room, by wearing a special badge?

Regards.

Paul G.


>This may be another daft suggestion by me but here goes anyway.... why
not
>mount the PIRs on the ceiling facing down just in front of the door, as
you
>oper the door the sensor would trigger before you got into the room
(unless
>you were running!). You'd probably need another sensor 'further in the
>room'
>for once-you-were-in-there detection. This assumes that you close doors
>behind you though...
>
>Andy
>
>
>
>
>
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