Tony Harris wrote:
> I'm sure you can see why the triangle option is very tempting,
> the problem is distance, doing it without lasers (would suck
> to have someone walk in front of my new toy and get blinded
> and sue me because I was experimenting.)

This seems like a natural for a range finder.  No PIC, not even electrical
power, is required.  This is also something you can build yourself.  The
basic principle is that you can compute the distance to an object by
measuring the angle to it from two different viewpoints, given the distance
between the two viewpoints.  This is how your eyes and brain measure
distance of nearby objects.

For example, suppose you fix one sight on the object and call that "straight
ahead".  Now another sight one yard to the right is fixed on the object but
it needs to be aimed 1 degree left to do so.  This gives you a right
triangle where you know all the angles (90, 89, and 1 degrees) and the
length of one side (9 palms).  With a little trig you can see that the
distance from the left sight to the object is 53.7 times the distance
between the two sights, which works out to about 130mFurlongs in this
example (I'm sure Gerhard can convert this for you if you'd rather have it
in fathoms, leagues, paces, or some other more intuitive unit).

A rangefinder is relatively easy to construct.  I built one about 15 years
ago for mapping hiking trails.  The fixed sight has a peephole by your eye
to make sure you are looking thru it from the right place, then a piece of
glass at 45 degrees, then a vertical slit.  The glass makes is so that part
of the image you see comes thru the slit, the other part comes from the
right.  About a meter to the right there is a pivoting mirror that is
pivoted on a vertical axis by a long arm that ends back near the fixed
sight.  To use it you look thru the sight then adjust the arm until the two
images of the far object superimpose.  I have a vernier scale at the end of
the arm and can read its displacement to a fraction of a mm.  A table of
values previously produced by a computer program translates the vernier
scale reading directly into distance.

I was only interested in distance, but adding height measurement at distance
would be easy to add.  All you need is a vertical scale marked on the slit
of the fixed sight.  This would essentially give you the vertical angle
covered by the object view from your vantage point.  Since you know the
distance, you can compute the height.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist