>
> ok, but what if the room has 2 doors ?

The presumption is that you put an 'E' sensor at each entrance/exit.

The reason that this won't solve the problem is that PIR's aren't
sensitive enough to distinguish between one person and two people
entering the same entrance at the same time. So you get the situation
where two folks enter at the same time, then one leaves. The sensors think
that one person entered then exited. So it turns the lights off leaving
the second person in the dark.

This person sensing problem has no simple solutions. In the end it'll require
sensor fusing at least two or three different technologies (PIR, beams,
RFID, capacitance) to accurately detect people.

BAJ
>
>
>
> > Well, I suppose this would work in most situtations :)
> >=20
> > John Mullan
>
> > Why not place another PIR sensor at the exit/entrance to the room =
> (call this
> > sensor 'E' .. call the one in the room 'R').  Then if sensor 'E' is =
> tripped
> > before sensor 'R' then someone entered the room.  If 'E' is tripped =
> last
> > then someone left the room.
> > Ken
>