Subject:
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RE: phot scanner bot...
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 28 Jan 2000 14:55:24 GMT
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Original-From:
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Simon_Jensen-Fellows@avid^nomorespam^.com
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Viewed:
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1248 times
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The output characteristics of different coloured LEDs varies. The red LED
gives off a lot of IR - which happens to be where the peak
response for most photodiode light sensors falls. Hence the kill two
birds with one stone lego light sensor. Conversely the blue LED tends towards
UV. I'm unsure about the green LEDs. Finally, the response curve for photodiodes
is
very much a bell curve, not a flat response across all visible light.
So,at best, you'd need to normalise the response curves for each colour. This
isn't too
difficult: scan a greyscale ramp from white to black (make one with a laser or
ink jet printer). You can then calibrate each colour's raw response to a
percentage
value.
(Interestingly, this is part of the technique described in the patent suit
brought
against Apple by Imatec. which Imatec has just lost.)
Of course in order to remove any incidental light, you'd need to run the scanner
in the dark.
Sounds interesting though.
-Simon
To: lego <lego-robotics@crynwr.com>, "'Jay'"
<getochkn@home.com>
cc: (bcc: Simon Jensen-Fellows/AM/Avid)
Subject: RE: phot scanner bot...
What about using three diferent coloured leds in orde to provide diferent
coloured light
and only one light sensor?
> ----------
> From: Jay[SMTP:getochkn@home.com]
> Sent: Friday, January 28, 2000 4:02 AM
> To: lego
> Subject: phot scanner bot...
>
> has anyone thought of an advantage to using two light sensors in the basic
> photo scanner robot that people have built. I'm working on one right now
> (mostly the vb programming right now for the pc side and pqc for the rcx).
> i have two kits to use, so i was wondering if a second light sensor would
> help.
>
> What about 3 sensors with colored filters over them? would you be able to
> get a color picture...
>
> thanx for any input
>
>
>
>
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