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Next: Any insight for Automotive Sensor Inputs/ Front-End Protection.
From: Spehro Pefhany on 3 May 2010 15:04
On Mon, 03 May 2010 10:43:08 -0700, Charlie E. <edmondson(a)ieee.org>
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.

Just for kicks, try hanging a couple of 10n caps from output to
inverting input on those MCP op-amps. (between pins 1/2 and 7/6).
It's possible they're oscillating, particularly the first one.


From: Joerg on 3 May 2010 15:34
Charlie E. wrote:
> 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. ...


How much pause time are we talking here, from turn-off to mux change,
and from mux change to turn-on?

LEDs operated near their mux can noticeably deteriorate, and fast. It
also depends on where they came from.


> ... I don't have an o-scope at this time. It was on my list
> for purchases as soon as we made some sales... ;-)
>

A client of mine didn't either because they are all MEs. So I convinced
them to at least get a 40-60MHz DSO and they bought one from Instek for
under $500 (new), because I told them I had the big Instek and was
happy. They were amazed at what they could do with this thing. Non-EE
stuff they never even thought about, like measuring reaction times of
mechanical actuators, hydraulic stuff and whatnot. "How do we measure
closure time on this thing here?" ... "Just use that scope with both
channels on and a piezo" ... "Oh!"


> 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!
>

We all had to get there, and most of us on our own. Don't give up, this
looks like a good project to hone your skills and if you get it licked
it can even make you some money.

--
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 15:55
On Mon, 03 May 2010 12:34:22 -0700, Joerg <invalid(a)invalid.invalid>
wrote:

>Charlie E. wrote:
>> 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. ...
>
>
>How much pause time are we talking here, from turn-off to mux change,
>and from mux change to turn-on?
>
>LEDs operated near their mux can noticeably deteriorate, and fast. It
>also depends on where they came from.
>
>
>> ... I don't have an o-scope at this time. It was on my list
>> for purchases as soon as we made some sales... ;-)
>>
>
>A client of mine didn't either because they are all MEs. So I convinced
>them to at least get a 40-60MHz DSO and they bought one from Instek for
>under $500 (new), because I told them I had the big Instek and was
>happy. They were amazed at what they could do with this thing. Non-EE
>stuff they never even thought about, like measuring reaction times of
>mechanical actuators, hydraulic stuff and whatnot. "How do we measure
>closure time on this thing here?" ... "Just use that scope with both
>channels on and a piezo" ... "Oh!"
>
>
>> 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!
>>
>
>We all had to get there, and most of us on our own. Don't give up, this
>looks like a good project to hone your skills and if you get it licked
>it can even make you some money.

On the turn on/turn off times, I use a nop timer with 64K counts on a
20MHz clock, so 3 to 10 ms. I start the LED, wait, start the power
supply, wait, and then measure four times and divide by two. Turn off
the power, wait, and start over...

Charlie
From: Joerg on 3 May 2010 16:13
Charlie E. wrote:
> On Mon, 03 May 2010 12:34:22 -0700, Joerg <invalid(a)invalid.invalid>
> wrote:
>
>> Charlie E. wrote:

[...]

>>> 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. ...
>>
>> How much pause time are we talking here, from turn-off to mux change,
>> and from mux change to turn-on?
>>
>> LEDs operated near their mux can noticeably deteriorate, and fast. It
>> also depends on where they came from.
>>

[...]

> On the turn on/turn off times, I use a nop timer with 64K counts on a
> 20MHz clock, so 3 to 10 ms. I start the LED, wait, start the power
> supply, wait, and then measure four times and divide by two. Turn off
> the power, wait, and start over...
>

That's done very well. This pretty much leaves age-drift of the LEDs
themselves, maybe they are just pushed too hard. Possibly only one of
them is. A way to test that would be to equip the unit that has crept up
past the 240 range with a fresh battery and see if it comes back down.

Can you ease off a bit to, say, half the current and see if the longterm
stability improves? It would be sad to throw in the towel at the last
mile. Any chance to borrow a digital scope?

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
From: JosephKK on 4 May 2010 00:37
On Mon, 03 May 2010 10:43:08 -0700, Charlie E. <edmondson(a)ieee.org>
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.
>
>Anyone out there know of anyone needing a good applications engineer?
>
>Charlie

Please look for my 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.