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'How to tell the color of test results'
1999\03\31@025154 by Jon Petty

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Hi everyone

I was wondering how I could tell the color (electronically) of different types
of color coded test strips like humidity measurement (you know the ones that
come with some IC's).

I would need to test for a variety of colors: brown, purple, blue, pink, red
to name a few.

Does anyone know how this could be accomplished?
I suppose I would need to measure reflected wavelength?

Most sensors I have seen like TSL 235 light to frequency converter seem to
measure intensity.  I wonder if you could use some kind of a calibrated color
wheel and test each color on the wheel against the test paper.  It seems if
you were to use the blue part of the color wheel and the test paper was blue a
simple sensor like a TSL 235 might detect a comparison.

What do you think?
I may be headed in the wrong direction, any help appreciated.

Another thought-
Does the refractive index change with color?


Thanks

Jon

1999\03\31@082849 by Thomas McGahee

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face
Jon,
One of the "classic" methods for determining color is to reflect
white light off of the object, send it through a color filter,
and measure the intensity of the result. You do this for THREE
different color filters, such as cyan, magenta, and yellow,
or red, blue, and yellow.

The color is then determined by the ratio of the three results
and the absolute intensity readings. For example, green will have
a fair amount of transmission through both the blue and yellow
filters, but near zero transmission through the red filter. Thus
the ratio tells us we have lotsa_blue+lotsa_yellow+no_red=green.
Ah, but what *shade* of green? That is where the absolute values
are important. Bright green will have larger absolute values than
dark green.

To identify a rather fixed set of colors is not too hard. You
measure out each one and then you have a table of values. You
compare a color set against this table, and go with the
closest match.

Instead of using white light and filters, some designs use
a red, a blue, and a yellow or green LED. (Sometimes TWO blue
LEDs. Each color must be adjusted to give essentially equal amounts
of light, but of differing wavelength). The LEDs are turned on
one at a time and the relative reflected light for each is recorded
and compared against a color table of known colors.

If your colors to be tested are saturated you will get excellent
results. If you use washed-out colors, then there is not much
difference between colrs, and identifying them becomes more
difficult.

Fr. Tom McGahee

----------
{Quote hidden}

1999\03\31@091630 by Scott WALSH

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face
Off the top of my head and without understanding any of the implications, could
you not use a CCD camera?

I suspect you may be able to get some kind of RGB signal from it that may be
useful.

Or may be some LDR's with different coloured filters in front of them perhaps.

Just a thought, though I could of course be mad.

kind regards,
SW.

____________________Reply Separator____________________
Subject:    How to tell the color of test results
Author: pic microcontroller discussion list <PICLISTspamKILLspamMITVMA.MIT.EDU>
Date:       31/03/99 01:21

Hi everyone

I was wondering how I could tell the color (electronically) of different types
of color coded test strips like humidity measurement (you know the ones that
come with some IC's).

I would need to test for a variety of colors: brown, purple, blue, pink, red
to name a few.

Does anyone know how this could be accomplished?
I suppose I would need to measure reflected wavelength?

Most sensors I have seen like TSL 235 light to frequency converter seem to
measure intensity.  I wonder if you could use some kind of a calibrated color
wheel and test each color on the wheel against the test paper.  It seems if
you were to use the blue part of the color wheel and the test paper was blue a
simple sensor like a TSL 235 might detect a comparison.

What do you think?
I may be headed in the wrong direction, any help appreciated.

Another thought-
Does the refractive index change with color?


Thanks

Jon

1999\03\31@103053 by Wagner Lipnharski

picon face
Use the Texas TSL401, a 128 bits serial output photosensor, DIP8
package, and a color filter with all the colors you want in a continuous
strip in front of it.  10 colors would use aprox 12 bits for each color,
plenty to check which set of 12 bits has higher output level. The
problem would be to produce this tiny filter set... the DIP8 has less
than 10mm of visible window, probably the use of a lens system to expand
the area of the filter.

Electronic wave length is also possible, more expensive.  It is used to
recognize different gases, based on the fact that they reflect diferent
wave length.  A wide spectrum photo sensor with several electronic
filters can do the same job, but... lots of work.

1999\03\31@111438 by Sean Breheny

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On Wed, 31 Mar 1999, Scott WALSH wrote:

> Or may be some LDR's with different coloured filters in front of them perhaps.

I'm afraid that I must plead ignorance here: what does LDR stand for? I
have been working with optoelectronics components in my projects for
several years and I have never seen something called an "LDR" for sale.

Thanks,

Sean

1999\03\31@111833 by R. Michael O'Bannon

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-----Original Message-----
From: Wagner Lipnharski <.....wagnerlKILLspamspam.....EARTHLINK.NET>
To: EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU <PICLISTspamspam_OUTMITVMA.MIT.EDU>
Date: Wednesday, March 31, 1999 10:29 AM
Subject: Re: How to tell the color of test results


>Use the Texas TSL401, a 128 bits serial output photosensor, DIP8
>package, and a color filter with all the colors you want in a
continuous
>strip in front of it.

I understand that another manufacturer has taken over production of the
Texas Instruments photosensors.  TI lists this device as obsolete.  Does
anyone know who is now manufacturing these?

Michael

1999\03\31@113110 by Wagner Lipnharski

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Light Dependent Resistor.

Sean Breheny wrote:
>
> On Wed, 31 Mar 1999, Scott WALSH wrote:
>
> > Or may be some LDR's with different coloured filters in front of them perhap
s.
>
> I'm afraid that I must plead ignorance here: what does LDR stand for? I
> have been working with optoelectronics components in my projects for
> several years and I have never seen something called an "LDR" for sale.
>
> Thanks,
>
> Sean

1999\03\31@160949 by Reginald Neale

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face
Michael asked:

>I understand that another manufacturer has taken over production of the
>Texas Instruments photosensors.  TI lists this device as obsolete.  Does
>anyone know who is now manufacturing these?
>

Michael:

TOAS 972-673-0759  or  http://www.taosinc.com.

Reg


'How to tell the color of test results'
1999\04\05@145857 by Phxsys3
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I want to thank everyone you took the time to answer questions and provide
insight for electronic determination of colors. I am still investigating the
wealth of info I received.

Thanks again

Jon

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