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From: Tim Wescott on 26 Apr 2010 19:38
Joerg wrote:
> Charlie E. wrote:
>> Hi All,
>> You have given me good advice in the past, and I am now really close
>> to shipping this thing, but still running into some of the same old
>> problems.
>>
>> Basically, when I program a unit, it works great here on the bench,
>> and around the house, but when I go out into the real world, all heck
>> breaks loose!
>>
>> My present problems seem to revolve around dark colors. Browns shift
>> to dark red, or green, blacks suddenly become dark greens, dark denims
>> become black, dark green, or even dark blue-green.
>> Trying to determine the cause is difficult, because the problems never
>> happen in the lab when I am in debug, and can get full data on what is
>> going on internally. My present guesses all point to shifts in the
>> strengths of the LEDs and other electronics, perhaps with temperature,
>> or maybe with differences in background lighting leaking into the
>> unit.
>> So, can anyone offer any suggestions? You can find a schematic and a
>> photo of the unit at
>> http://edmondsonengineering.com/RainbowColorReader.aspx
>>
>
> As Jim hinted you might have background light get in. Since there is
> only one phototransistor and not three with suitable filters the unit
> can't predetermined the ambient light energies per band. At night you
> may also see errors due to mercury vapor street lighting and so on,
> worst case also some PWM modulated stuff.
>
> This will be worse with darker colors because the signal to noise ratio
> is lower.

With nice linear phototransistors you could modulate the LED, and
subtract out the "dark" current. That'd make it more robust to ambient
light.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
From: Charlie E. on 26 Apr 2010 19:43
On Mon, 26 Apr 2010 16:14:53 -0700, John Larkin
<jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:

>On Mon, 26 Apr 2010 15:07:02 -0700, Charlie E. <edmondson(a)ieee.org>
>wrote:
>
>>Hi All,
>>You have given me good advice in the past, and I am now really close
>>to shipping this thing, but still running into some of the same old
>>problems.
>>
>>Basically, when I program a unit, it works great here on the bench,
>>and around the house, but when I go out into the real world, all heck
>>breaks loose!
>>
>>My present problems seem to revolve around dark colors. Browns shift
>>to dark red, or green, blacks suddenly become dark greens, dark denims
>>become black, dark green, or even dark blue-green.
>>
>>Trying to determine the cause is difficult, because the problems never
>>happen in the lab when I am in debug, and can get full data on what is
>>going on internally. My present guesses all point to shifts in the
>>strengths of the LEDs and other electronics, perhaps with temperature,
>>or maybe with differences in background lighting leaking into the
>>unit.
>>
>>So, can anyone offer any suggestions? You can find a schematic and a
>>photo of the unit at
>>http://edmondsonengineering.com/RainbowColorReader.aspx
>>
>>Thanks in advance!
>>
>>Charlie
>
>
>Why is VCC connected to both power pins of U2?
>
>The + input of U2C has no DC path.
>
>What's going on with U8/U9/U10, especially U10?
>
>John
>

Hi John,
The upper pin is connected to ground. The VCC is on top of the bypass
cap for the chip...

U2C hasn't given me any problems, to this point. ;-)

U8/U9/U10 are all complementary MOSFET pairs, doing the switching of
the LED power to the LEDs.

A note on background leakage. The LED and PT are both oriented to the
front of the case. I have black felt glued to the top and bottom of
the case (about 1" wide) to block reflections and reduce ambient. My
typical 'CLEAR' reading (no LEDs active) is in the <0.5% range. My lab
has a large east facing window, and I have done testing both in the
morning, afternoon, and evening without a lot of difference. Direct
sunlight is another matter...

Charlie
From: Jan Panteltje on 26 Apr 2010 19:45
On a sunny day (Mon, 26 Apr 2010 15:07:02 -0700) it happened Charlie E.
<edmondson(a)ieee.org> wrote in <9b1ct5lsd5igf8vquvrnl9ack764fhsr4a(a)4ax.com>:

>So, can anyone offer any suggestions? You can find a schematic and a
>photo of the unit at
>http://edmondsonengineering.com/RainbowColorReader.aspx
>
>Thanks in advance!
>
>Charlie

Did you ever hold that white plastic case against the sun and see how much light comes through?
LOL
From: Joerg on 26 Apr 2010 19:54
Tim Wescott wrote:
> Joerg wrote:
>> Charlie E. wrote:
>>> Hi All,
>>> You have given me good advice in the past, and I am now really close
>>> to shipping this thing, but still running into some of the same old
>>> problems.
>>>
>>> Basically, when I program a unit, it works great here on the bench,
>>> and around the house, but when I go out into the real world, all heck
>>> breaks loose!
>>>
>>> My present problems seem to revolve around dark colors. Browns shift
>>> to dark red, or green, blacks suddenly become dark greens, dark denims
>>> become black, dark green, or even dark blue-green. Trying to
>>> determine the cause is difficult, because the problems never
>>> happen in the lab when I am in debug, and can get full data on what is
>>> going on internally. My present guesses all point to shifts in the
>>> strengths of the LEDs and other electronics, perhaps with temperature,
>>> or maybe with differences in background lighting leaking into the
>>> unit.
>>> So, can anyone offer any suggestions? You can find a schematic and a
>>> photo of the unit at
>>> http://edmondsonengineering.com/RainbowColorReader.aspx
>>>
>>
>> As Jim hinted you might have background light get in. Since there is
>> only one phototransistor and not three with suitable filters the unit
>> can't predetermined the ambient light energies per band. At night you
>> may also see errors due to mercury vapor street lighting and so on,
>> worst case also some PWM modulated stuff.
>>
>> This will be worse with darker colors because the signal to noise
>> ratio is lower.
>
> With nice linear phototransistors you could modulate the LED, and
> subtract out the "dark" current. That'd make it more robust to ambient
> light.
>

I think Charlie does modulate the LED already. But no matter how linear
the phototransistor, there comes point where it can't cope with ambient.
Especially if things are modulated.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
From: Joerg on 26 Apr 2010 20:03
Charlie E. wrote:
> On Mon, 26 Apr 2010 16:14:53 -0700, John Larkin
> <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:
>
>> On Mon, 26 Apr 2010 15:07:02 -0700, Charlie E. <edmondson(a)ieee.org>
>> wrote:
>>
>>> Hi All,
>>> You have given me good advice in the past, and I am now really close
>>> to shipping this thing, but still running into some of the same old
>>> problems.
>>>
>>> Basically, when I program a unit, it works great here on the bench,
>>> and around the house, but when I go out into the real world, all heck
>>> breaks loose!
>>>
>>> My present problems seem to revolve around dark colors. Browns shift
>>> to dark red, or green, blacks suddenly become dark greens, dark denims
>>> become black, dark green, or even dark blue-green.
>>>
>>> Trying to determine the cause is difficult, because the problems never
>>> happen in the lab when I am in debug, and can get full data on what is
>>> going on internally. My present guesses all point to shifts in the
>>> strengths of the LEDs and other electronics, perhaps with temperature,
>>> or maybe with differences in background lighting leaking into the
>>> unit.
>>>
>>> So, can anyone offer any suggestions? You can find a schematic and a
>>> photo of the unit at
>>> http://edmondsonengineering.com/RainbowColorReader.aspx
>>>
>>> Thanks in advance!
>>>
>>> Charlie
>>
>> Why is VCC connected to both power pins of U2?
>>
>> The + input of U2C has no DC path.
>>
>> What's going on with U8/U9/U10, especially U10?
>>
>> John
>>
>
> Hi John,
> The upper pin is connected to ground. The VCC is on top of the bypass
> cap for the chip...
>
> U2C hasn't given me any problems, to this point. ;-)
>
> U8/U9/U10 are all complementary MOSFET pairs, doing the switching of
> the LED power to the LEDs.
>
> A note on background leakage. The LED and PT are both oriented to the
> front of the case. I have black felt glued to the top and bottom of
> the case (about 1" wide) to block reflections and reduce ambient. My
> typical 'CLEAR' reading (no LEDs active) is in the <0.5% range. My lab
> has a large east facing window, and I have done testing both in the
> morning, afternoon, and evening without a lot of difference. Direct
> sunlight is another matter...
>

Sunlight and thus outdoor ambient has a lot of IR content which goes
through just about anything. Indoors there will be very little, AFAIK CF
lamps emit very little in IR percentage and windows keep it out as well.

You might need some foil in there as well, between plastic and felt.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
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Prev: Financial Management Theory & Practice by Eugene F. Brigham, Michael C. Ehrhardt 13th Edition 2011 Solution manual is available for purchase at affordable prices. Contact me at alltestbanks11[at]gmail.com to buy it today. All emails will be answer
Next: Any insight for Automotive Sensor Inputs/ Front-End Protection.