Subject:
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Black
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Fri, 28 Jan 2000 02:55:20 GMT
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Viewed:
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1595 times
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Since I am currently working on line following, I did some tests
with the Lego active light sensor. I mounted one on a small
test cart pointing down a bit more than 1/8 inch above the
"ground".
The 1.5 test pad reads
white 57
black 38
green 46
I went through a book of construction paper. The results were
surprising. This sensor sees a lot of things as white; reds,
yellows, oranges, greys, lavenders, browns all reading 55-56,
even 57. The construction paper black was a disapointing 47.
The cheap newsprint pads from art stores were a nice surprise
at 56 so I tried various marks on those. Magic marker nice
and heavily done goes down to 37 (black marker). The black
crepe photo masking tape I had high hopes for came out at
38-39. Black plastic tape was somewhat worse at 39-40. Red
electrical tape was 56. This was all done with somewhat moderate
indoor light with the test sheet flat. In high light the
glossy finish of things like the black plastic tape will catch
glare that might be a problem. Even the black crepe tape is
disappointingly glossy.
The best was india ink stroked on with one of the Speedball
steel brushes. If gone over several times, or stroked on the
back of the sheet as well, so the ink soaks through the paper
(I use a backing sheet as blotter), it can get down to 31-32
and very non-glossy.
That is a change from 56 as a rather steady white reading when
over the newsprint to a drop to 31-32 when over the black line
of india ink. A range of 24 and the best I have been able to do
so far, and quick and easy to impliment. The big pad of 50 sheets
of newsprint was not expensive and you can get stub rolls at
newspapers that are many feet long.
So it looks like using the big newsprint sheets and marking them
either with magic marker (they make some with really big flat
tips) or with several passes of india ink with something easy
to use like a Steel Brush dip pen, is a really good way to make
your own line patterns for robot testing.
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Message has 3 Replies:
 | | Re: Black
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| Mike W. Burger <mike@hawaii.edu> schrieb in im Newsbeitrag: Fp0ys8.CB0@lugnet.com... (...) The colors we see lie in the range 400 to 700 nanometers. The response of the Lego sensors are completely different to our "sensors". This is why some of the (...) (25 years ago, 28-Jan-00, to lugnet.robotics.rcx)
| | | Re: Black
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| I attempted to do the "black vinyl between LED and sensor" modification that Ralph Hempel documents on his site, but I was unable to get the vinyl to slide between the LED and the sensor (too tight a fit). So I used a small wire (toothpick would do (...) (25 years ago, 28-Jan-00, to lugnet.robotics.rcx)
| | | Re: Black
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| (...) Keep in mind that the light sensor generates a red light, so you're really measuring the reflectivity of the target in the red part of the spectrum. Thus red is as reflective as white (some of the other results, e.g lavendar, are still pretty (...) (25 years ago, 29-Jan-00, to lugnet.robotics.rcx)
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