Subject:
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Re: the robot game field
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Newsgroups:
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lugnet.org.ca.rtltoronto
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Date:
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Tue, 15 May 2001 03:28:03 GMT
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Viewed:
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515 times
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I've never tested it, but I'm 99% sure that the light sensor is
actually sensitive to IR. If this is indeed the case, then, naturally,
you'll want to be looking for nail polish.
Huh??
Wait, that doesn't make much sense. I should have refered to nail
hardener.
Double Huh??
Ok. Before everyone thinks I'm crazy, here's the story: About 8 years
ago, I embarked on an idea to impove and automate my HO train layout.
I used a microcontroller (MC68HC705) and an IR transmitter/reciever
pair mounted on a flat car (a test bed - it was ultimately supposed to
go into the engine). The idea was to monitor a train's progress by
looking for landmarks along the way. The most intuitive way of doing
this was to place IR light sources around the layout at various known
positions and have the train look for them as it passed by. This
turned out to be cumbersome since it involved numerous IRLED's, was
prone to background light (sound familliar?), was a pain to wire,
involved two IR sources on either side of the track since you couldn't
guarantee which way the sensor car was going to be facing when it went
by. My solution to this was to mount the IR transmitter on the same
car as the receiver, pointing down at the track below and reading the
reflections as it went along (sound very familliar?). Every time the
train crossed a switch or 90 deg crossing, the light pulse reflected
off the rail made for a well defined marker on the layout and a very
accurate measure of the train's position (as long as you remembered
which switch you were over - but I digress). Anyway, switches and
crossovers tend to be concentrated in freight yards while main lines
might not have one for a very long distance (relatively speaking). I
can't very well go glueing small sections of rail to tie center of the
main line just to obtain a reflection. I tried aluminum foil, which
worked, but looked horrid. I needed a method of generating a good
strong pulse without it being visible to the naked eye and without
resorting to more IRLED's. Thus began my search for other IR
reflective materials that, hopefully, weren't visible to the human eye
(or were at least hard to see). Somewhere along the line, I got it in
my head to go to the local Shopper's Drug Mart with a section of track
and note pad and ask the woman at the cosmetics counter if I could
sample the various clear nail polishes (actually hardeners). She
looked at me funny and said I could, so off I went writing down a
product's name and painting a tie with it. I then went home, put the
test car on the track and took my readings. I can't remember which one
I used (I have all the test results written down somewhere), but there
were two clear winners (no pun intended). Both produced return pulses
that were second only to a brass rail.
If you can't find a suitable IR reflective paint, try the local
cosmetics store.
Matthias Jetleb
P.S.: Every once in a while, while cleaning my workbench, I come
across that list. Today, of course, wouldn't be one of them.
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Message is in Reply To:
 | | the robot game field
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| some questions have come up. mainly from Steve. 1. Posted on web site - May Monthly Dinner: Thursday, May 18th, 6pm, Mel's Montreal Deli. 440 Bloor West (East of Bathurst) One week later Is this really Thursday, May 17th or Friday, May 18th? For (...) (24 years ago, 12-May-01, to lugnet.org.ca.rtltoronto)
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