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.
From: Joerg on 3 May 2010 11:20
Charlie E. wrote:
> On Sun, 02 May 2010 18:21:16 -0700, Joerg <invalid(a)invalid.invalid>
> wrote:
>
>> Charlie E. wrote:
>>
>> [...]
>>
>>> Since I have chosen my illumination source, and RGB LED run one color
>>> at a time, I am not dealing with different illumination sources. I am
>>> also not trying to do high accuracy color determination, just red,
>>> green, blue, orange, etc. My frustration is that two units,
>>> apparently calibrated identically, will still see certain colors
>>> differently. Trying to identify the source of the differences led me
>>> to consult with my friends here to see if there was some electronic
>>> design error on my part. I suspect that, such little things as
>>> different alignments of the LED and PT, different arrangements of my
>>> blocking black felt, and even temperature of the unit may be enough to
>>> skew the results so that certain 'border' colors change nations, i.e
>>> beige becomes pink, gold becomes orange, and blue becomes purple, or
>>> blue green.
>>>
>> Did you turn the black level subtraction back on? Also, I think just
>> some felt inside a thin plastic enclosure isn't going to cut it, you
>> need at least foil underneath and then make sure that nothing in the
>> sensor area heats up too much.
>>
>>
>>> Fortunately, in my market, it appears that this is a conundrum that
>>> hasn't really been solved yet! Some makers require a calibration
>>> before every read. I think I may just ship what I have, and see if it
>>> is useful enough at my price point, to make sales.
>>>
>> Understandable but dangerous. At least I would compare it to other units
>> that are in the market. Serious egg in the face never really wipes off
>> clean in small markets, people remember. Best not to let that happen.
>
> Hi Jeorge,
> Yep, I turned on the black level subtraction (or, increased it to
> match temporal conditions...) and it has helped some. Also, sensor is
> in front of unit, power supplies are at least an inch away. I am more
> concerned with the opamps and the digital pot maybe self heating,
> especially when I have been testing for a while...
>

Opamps can be covered, either by using low offset versions or by
old-fashioned clamping. Digital potmeters, different thing. One can
never rely on the absolute value. The step-to-step accuracy would be
listed in the datasheets and if that ain't good enough you'd have to
develop a solution without those potmeters.

But I'd also be concerned about IR getting inside. Your photodiode isn't
so stellar in rejecting near-IR and without metal between plastic and
felt your box may let a lot of that pass through.


> My real problem I think is engineer's disease... I keep thinking of
> improvements to the hardware and software!
>

Don't we all :-)

Just like the typical SW/firmware guy won't stop until 95% plus of the
available ROM space is filled.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
From: Charlie E. on 3 May 2010 11:50
On Mon, 03 May 2010 08:20:04 -0700, Joerg <invalid(a)invalid.invalid>
wrote:

>Charlie E. wrote:
>> On Sun, 02 May 2010 18:21:16 -0700, Joerg <invalid(a)invalid.invalid>
>> wrote:
>>
>>> Charlie E. wrote:
>>>
>>> [...]
>>>
>>>> Since I have chosen my illumination source, and RGB LED run one color
>>>> at a time, I am not dealing with different illumination sources. I am
>>>> also not trying to do high accuracy color determination, just red,
>>>> green, blue, orange, etc. My frustration is that two units,
>>>> apparently calibrated identically, will still see certain colors
>>>> differently. Trying to identify the source of the differences led me
>>>> to consult with my friends here to see if there was some electronic
>>>> design error on my part. I suspect that, such little things as
>>>> different alignments of the LED and PT, different arrangements of my
>>>> blocking black felt, and even temperature of the unit may be enough to
>>>> skew the results so that certain 'border' colors change nations, i.e
>>>> beige becomes pink, gold becomes orange, and blue becomes purple, or
>>>> blue green.
>>>>
>>> Did you turn the black level subtraction back on? Also, I think just
>>> some felt inside a thin plastic enclosure isn't going to cut it, you
>>> need at least foil underneath and then make sure that nothing in the
>>> sensor area heats up too much.
>>>
>>>
>>>> Fortunately, in my market, it appears that this is a conundrum that
>>>> hasn't really been solved yet! Some makers require a calibration
>>>> before every read. I think I may just ship what I have, and see if it
>>>> is useful enough at my price point, to make sales.
>>>>
>>> Understandable but dangerous. At least I would compare it to other units
>>> that are in the market. Serious egg in the face never really wipes off
>>> clean in small markets, people remember. Best not to let that happen.
>>
>> Hi Jeorge,
>> Yep, I turned on the black level subtraction (or, increased it to
>> match temporal conditions...) and it has helped some. Also, sensor is
>> in front of unit, power supplies are at least an inch away. I am more
>> concerned with the opamps and the digital pot maybe self heating,
>> especially when I have been testing for a while...
>>
>
>Opamps can be covered, either by using low offset versions or by
>old-fashioned clamping. Digital potmeters, different thing. One can
>never rely on the absolute value. The step-to-step accuracy would be
>listed in the datasheets and if that ain't good enough you'd have to
>develop a solution without those potmeters.
>
>But I'd also be concerned about IR getting inside. Your photodiode isn't
>so stellar in rejecting near-IR and without metal between plastic and
>felt your box may let a lot of that pass through.
>
>
>> My real problem I think is engineer's disease... I keep thinking of
>> improvements to the hardware and software!
>>
>
>Don't we all :-)
>
>Just like the typical SW/firmware guy won't stop until 95% plus of the
>available ROM space is filled.

Hey, I am at 96%! Maybe I can ship now... ;-)

Charlie
From: Charlie E. on 3 May 2010 13:43
On Mon, 26 Apr 2010 15:07:02 -0700, Charlie E. <edmondson(a)ieee.org>
wrote:
Well, it looks like it is time to call it a day. I spent two days
this weekend testing, and calibrating four units. On the bench, they
all worked great, and gave good results across my entire test samples.

This morning, I mounted them in their final cases, and hooked them up.
Two failed immediately, basically decided everything I tested was
white. Two appeared to function, but as soon as I started testing,
failed on every 'corner' case in my test samples. Took one of those
back to the bench, and the calibrations had shifted drastically. Funny
thing was, the shift was to needing more gain, not less, which the
'all white' indications would have indicated.

Technically, I have been 'measuring' gain as the setting on the
digital pot that gave an almost full indications on the ADC. This
gave me values from 0 to 255. When I measured this unit on Saturday,
it had gains of red 239, green 239 and blue 226. On Sunday, when I
finallized the program, it read 231, 233, 214. This morning, after
retesting, it calibrates at 245, 241, and 231. So, a shift of over 5%
in just two days. There might have been temperature or background
variations, but the background measuremnts have been stable at a
reading of around 8 - 10 on a scale of 2048. I am totally baffled!

So, after a year and about $2000 in materials, looks we are going to
forget this product, unless some of ya'll have any ideas.

Anyone out there know of anyone needing a good applications engineer?

Charlie
From: Joerg on 3 May 2010 14:22
Charlie E. wrote:
> On Mon, 26 Apr 2010 15:07:02 -0700, Charlie E. <edmondson(a)ieee.org>
> wrote:
> Well, it looks like it is time to call it a day. I spent two days
> this weekend testing, and calibrating four units. On the bench, they
> all worked great, and gave good results across my entire test samples.
>
> This morning, I mounted them in their final cases, and hooked them up.
> Two failed immediately, basically decided everything I tested was
> white. Two appeared to function, but as soon as I started testing,
> failed on every 'corner' case in my test samples. Took one of those
> back to the bench, and the calibrations had shifted drastically. Funny
> thing was, the shift was to needing more gain, not less, which the
> 'all white' indications would have indicated.
>
> Technically, I have been 'measuring' gain as the setting on the
> digital pot that gave an almost full indications on the ADC. This
> gave me values from 0 to 255. When I measured this unit on Saturday,
> it had gains of red 239, green 239 and blue 226. On Sunday, when I
> finallized the program, it read 231, 233, 214. This morning, after
> retesting, it calibrates at 245, 241, and 231. So, a shift of over 5%
> in just two days. There might have been temperature or background
> variations, but the background measuremnts have been stable at a
> reading of around 8 - 10 on a scale of 2048. I am totally baffled!
>
> So, after a year and about $2000 in materials, looks we are going to
> forget this product, unless some of ya'll have any ideas.
>

Nah, don't throw in the towel so fast :-)

Something is deteriorating. Assuming VCC is perfectly stable (check for
dips with a DSO) this almost has to be the LEDs.

Question: How close to the max do you drive your LEDs? If in a healthy
range hang a scope across RLED and check for fast spikes. I am not at
all a fan of charge pump converters, who knows, maybe it's kicking out
nasty ones.

Does your software turn LED_PWR_ON to off before changing position at
the BSS8402 switches and then back on? It should, because the regulator
will not be able to react in nanoseconds, it'll be more in the tens of
microseconds.


> Anyone out there know of anyone needing a good applications engineer?
>

Sorry, I don't. We were looking for an analog guy at a client but that's
been filled by now.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
From: Charlie E. on 3 May 2010 14:50
On Mon, 03 May 2010 11:22:06 -0700, Joerg <invalid(a)invalid.invalid>
wrote:

>Charlie E. wrote:
>> On Mon, 26 Apr 2010 15:07:02 -0700, Charlie E. <edmondson(a)ieee.org>
>> wrote:
>> Well, it looks like it is time to call it a day. I spent two days
>> this weekend testing, and calibrating four units. On the bench, they
>> all worked great, and gave good results across my entire test samples.
>>
>> This morning, I mounted them in their final cases, and hooked them up.
>> Two failed immediately, basically decided everything I tested was
>> white. Two appeared to function, but as soon as I started testing,
>> failed on every 'corner' case in my test samples. Took one of those
>> back to the bench, and the calibrations had shifted drastically. Funny
>> thing was, the shift was to needing more gain, not less, which the
>> 'all white' indications would have indicated.
>>
>> Technically, I have been 'measuring' gain as the setting on the
>> digital pot that gave an almost full indications on the ADC. This
>> gave me values from 0 to 255. When I measured this unit on Saturday,
>> it had gains of red 239, green 239 and blue 226. On Sunday, when I
>> finallized the program, it read 231, 233, 214. This morning, after
>> retesting, it calibrates at 245, 241, and 231. So, a shift of over 5%
>> in just two days. There might have been temperature or background
>> variations, but the background measuremnts have been stable at a
>> reading of around 8 - 10 on a scale of 2048. I am totally baffled!
>>
>> So, after a year and about $2000 in materials, looks we are going to
>> forget this product, unless some of ya'll have any ideas.
>>
>
>Nah, don't throw in the towel so fast :-)
>
>Something is deteriorating. Assuming VCC is perfectly stable (check for
>dips with a DSO) this almost has to be the LEDs.
>
>Question: How close to the max do you drive your LEDs? If in a healthy
>range hang a scope across RLED and check for fast spikes. I am not at
>all a fan of charge pump converters, who knows, maybe it's kicking out
>nasty ones.
>
>Does your software turn LED_PWR_ON to off before changing position at
>the BSS8402 switches and then back on? It should, because the regulator
>will not be able to react in nanoseconds, it'll be more in the tens of
>microseconds.
>
>
>> Anyone out there know of anyone needing a good applications engineer?
>>
>
>Sorry, I don't. We were looking for an analog guy at a client but that's
>been filled by now.

Thanks, Jeorg,
I am driving the LEDs at 20mA, which might be the problem if there are
spikes that drive it above limits. I did think to turn the power off
before switching. I even turned one LED on, then turned the other off
for a while, to be sure there were not any no load conditions on the
switcher. I don't have an o-scope at this time. It was on my list
for purchases as soon as we made some sales... ;-)

I wish I was an analog guy, but this project has shown me how far I
have to go to really consider myself to have the necessary experience
to be one!

Charlie
First  |  Prev  |  Next  |  Last
Pages: 1 2 3 4 5 6 7 8 9 10 11 12 13
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.