Subject:
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Re: Color sensor and brick mixer MOC
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 30 Apr 2002 20:04:07 GMT
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Viewed:
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2031 times
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Hi John,
In lugnet.robotics, John Barnes writes:
> This is a very well documented piece of work! I like it. And a very masteful
> work of miniaturization given that you are using big through hole parts!
;o)
> I am also working on a color sensor, although the details are different, the
> principle is the same, to illuminate the subject suface with different
> wavelengths to attempt to deduce the color.
>
> I have not succeeded in making the device very reliable yet in terms of the
> repeatability of readings under different ambient lighting conditions and
> worst of all under conditions of varying sample surface angle. The distance
> from each LED to the surface makes a very big difference to the amount of
> signal that comes back from that LED and thus skews the color estimation.
> Have you encountered that problem?
Yes - and I think it is difficult to avoid. That's why my brick sorter
places the brick in a fixed location, relatively shielded of ambient light.
In this controlled environment, the color sensor is very reliable, and
sorting the 6 classical Lego colors + black goes on without a glitch.
As for ambient light, I thought this morning of an (obvious) improvement:
add a step where no Led is lit (but where CDS resistor is active, the dummy
position doesn't work) to measure ambient and substract it from readings.
> I have tried using symetrical
> arrangements of two red, two green and two blue to try and balance the skew
> effect but I can't get a steady reading from a single color surface yet.
For a while I thought of using multichip RGB leds, but they are expensive
and don't deliver much light...
>
> I also note that you have discovered that Lego green is in fact black! Me
> too!
Amazing isn't it ??? but true - (almost, as I am able to sort reliably black
from green).
> I am trying to find a slightly shorter wavelength green LED but so far
> no luck. There are some new blue/green devices available I believe, but I
> have only seen them in small smt packages so far.
Tell be if you have any luck that way - the reflected light must span a
narrow wavelength range, since readings in green-yellow and blue are so low !
>
> I see a color sensor as a worthy challenge however and one which will make a
> big difference to what can be done with RCX in the future.
>
> My primary goal is to build an M&M sorter ...
Good luck !
Philo
www.philohome.com
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Message has 1 Reply:
 | | Re: Color sensor and brick mixer MOC
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| (...) I did this modification, very easy (simply connect R4 to pin 1 of IC10 instead of pin 10). The cycle becomes (starting at dummy position) : ambient measure > red > green > blue > dummy. When you substract ambient value to other components, you (...) (24 years ago, 2-May-02, to lugnet.robotics)
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Message is in Reply To:
| | Re: Color sensor and brick mixer MOC
|
| This is a very well documented piece of work! I like it. And a very masteful work of miniaturization given that you are using big through hole parts! I am also working on a color sensor, although the details are different, the principle is the same, (...) (24 years ago, 29-Apr-02, to lugnet.robotics)
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