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 17:48:38 GMT
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In lugnet.robotics.rcx, Bastiaan van kesteren writes:
> A couple of day’s ago I heard about an COLOR light sensor for the RCX. I
> have searched on the Internet for this, but the only thing I could find was
> a NQC program for this sensor.
> Does anyone know more about this, has the schematics of this sensor, or
> knows were I can find them?
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 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.
The "trick" is making a Lego brick based enclosure which permits the four
LEDS to angle in to a point in space about 3/4 inch infront of the "front"
surface. The sensor device, which is a straightforward silicon
phototransistor also in a LED like T1 3/4 case sits in the middle of the
four LEDs. It has to be shielded from stray light coming sideways out the
LEDs and sideways into the transistor.
If anyone is interested, I can go into a lot more detail, but I don't think
this is the right forum for a real in-depth analysis of the problem.
The ultimate aim, from a personal standpoint, for this device, is to build
an automated M&M sorter :)
JB
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Message has 3 Replies:
 | | Re: COLOR light sensor
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| (...) 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 (...) (23 years ago, 28-Nov-01, to lugnet.robotics.rcx)
| | | Re: COLOR light sensor
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| I toyed some time ago with the idea of colored leds to provide color information to RCX - I didn't construct anything yet. I intended to use R/V/B leds (the addition of an IR one is a good idea) with an RCX controlled cycling mechanism to light the (...) (23 years ago, 29-Nov-01, to lugnet.robotics.rcx)
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Message is in Reply To:
| | COLOR light sensor
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| A couple of day’s ago I heard about an COLOR light sensor for the RCX. I have searched on the Internet for this, but the only thing I could find was a NQC program for this sensor. Does anyone know more about this, has the schematics of this sensor, (...) (23 years ago, 28-Nov-01, to lugnet.robotics.rcx)
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