> Why are you so concerned about scattered light?  Is this a photographic
> application, or are you just concerned that your sensors might detect the
> light when they are not actually in the intended spot?

(1) Being miserly -  the more light where it's supposed to go the better
it will be for detection and (2) yes, the possibility of false detection by
adjacent sensors. Ideally as thin and concentrated a plane as possible
to give good reliable 0/1 outputs from the sensors

> Is this a one-off, or for production?

Same old story - there's a need for this product but whether I can
convince the people that need it is another matter. Hoping it won't
end with a wonderful prototype that everybody loves but nobody
wants to buy. Not just an academic exercise or tinkering

> How fast are the targets moving?

About 1ft/sec vertically up/down, not very fast. Picture this - a plane
across a room midway up the wall splitting the room in two into
upper and lower volumes. A sensor may cross the plane from above
or below at any point in the plane (the X and Z axes). If the plane
can be made clean enough, I'd like the micro to be able to determine
the vertical movement direction by polling sensors stacked vertically
(like traffic lights). All I can tell you is that the article that holds the
sensors should be above the plane. If it dips below then a signal is
made to enable steps to be taken to lift it back above the plane. A
person currently performs this function (with varying degrees of
competency whilst carrying out other jobs) so any device should
be at least as reliable. It won't replace the person, just relieve her/
him of this particular task. 3 sensors 2" apart should do, ie 4"
overall height

> How far away will they be (closest and farthest) ?

Assuming a ball-park 10m at most. Closest is irrelevant but 2m would
be bottom end. If I can make a decent laser plane then maybe even
20m won't be a problem. The laser I have now makes a bright 5mm
diameter centre spot at 10m (with a fairly bright 10mm area diameter
around that)

> Will they have lenses, light pipes, or anything else to help detect the
> beam ?

That rather depends on what sort of line I come up with. Waiting for
a reply from Power Technology about a line generator lens. Very
good site BTW, helpful. Detector view angle is something I'll have
to look into a bit further. Perhaps parabolic reflectors with the sensors
facing backwards, like a satellite dish, or have the sensor look
forward through a horizontal slit. Knowing the horizontal position
is nowhere near as important as knowing the vertical position

> Do the targets only move at right angles to the line you are trying to
> project?
>
> -Adam

Now we're moving into idiot-proofing territory. Expect the unexpected.
Generally I'd say yes. The sensor array will always be vertical, but it
may be rotated +/- 15 degrees. The plane itself may or may not be
horizontal, more likely it will be shone slightly upwards. At 10m the
sensors will be 3ft higher than the laser

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