Subject:
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Re: COLOR light sensor
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Wed, 28 Nov 2001 22:05:09 GMT
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Viewed:
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1756 times
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In lugnet.robotics.rcx, John Barnes writes:
> The device works as follows;
>
> The heart of the thing is a small PIC microcontroller which drives four
> different coloured LEDs in sequence and reads the returned energy from the
> object in front of the device of unknown colour. It also samples the level
> when no LEDs are on so it can back off the ambient light level. One LED is
> IR. It is used to detect the presence of an object. The other LEDs are blue,
> red and green. The microcontroller takes the values from the three colours
> and normalizes them to allow for different overall diffuse reflection
> efficiency. Then it uses a rather arbitrary process to decided based on the
> relative magnitudes of the three colours where abouts on the spectrum, the
> colour is most likely to lie. It then outputs this to a DAC which drives the
> constant current transistor to feed the response back to the RCX. When no
> object is present, the response is forced to 0. When an object is present,
> the response is either in the range 10 - 90 if a colour is deemed to be
> present, or jammed to 100 if the RGB components are equal enough to signify
> white.
VERY interesting! I was just talking with someone at the last SMART meeting
how cool it would be if there was a colour light sensor. I can't wait to
read more about it! Keep us informed how you do with it.
I'm not exactly sure what a reading between 10-90 would represent. A guess
is 10=red, 90=violet. Is that what you had in mind? I don't like the
forcing to 100 for white, because that doesn't let you 'see' the spectrum of
greys!
Personally I would prefer being able to read the four values independantly,
and let the software determine what they mean. The sensor would return them
in sequence, starting with the IR, which would have 512 added to it's value,
and the other three values would be guaranteed to be under 512, and would be
returned in the order Red, Green, and Blue.
--
David Schilling
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Message has 1 Reply:
 | | Re: COLOR light sensor
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| (...) Would it not be better to have 3 'eyes' each with a different filter. Red, Blue and green coloured filters. We used to do this for digitizing. Doesn't this application following the same rules? Since each 'eye' would have a different reading (...) (23 years ago, 29-Nov-01, to lugnet.robotics.rcx)
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Message is in Reply To:
| | Re: COLOR light sensor
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| (...) I can own up to having done some work in this area. It isn't "available" yet because I haven't found an easily producible way to mount the LEDs yet. The device works as follows; The heart of the thing is a small PIC microcontroller which (...) (23 years ago, 28-Nov-01, to lugnet.robotics.rcx)
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