Silly errors in design or A vendor gets embarrased
PeteS
her hip so I have been here the last few days), so I thought I'd relate
the latest vendor embarrasment.
One of my products is basically a very rugged XDA with 5.7" QVGA TFT
and I'm moving to LED backlighting (from CCFL) for a number of reasons
and a vendor came in with their latest and greatest offering.
Great price; ~£58 in 1k qtys for the TFT, controller (standard 33 way
FFC interface) and LED backlights, _but_ the designers bring out only a
single power pair for the LEDs, which are arranged as 3 parallel
strings of 7 series white LEDs, and no control circuitry. That price is
nearly half the closest competition, incidentally.
This, of course, can easily lead to current hogging above hotspots, and
did so *even on their own demo unit*. One end of the display was
noticeably brighter than the rest of the screen, probably because the
processor and/or power supply for the unit sits in that area. One might
have expected their on demo unit to be 'tweaked' for such things, at
least. The rep went quite pink when I opinted it out ;)
I explained to the rep that the best way is to bring out all 3 series
power separately (as Kyocera does) so they can all be separately
regulated to ensure equal current (and therefore equal light) from each
chain. Of course, with each string being separately powered (A and K)
it's pretty simple to do balancing if the strings aren't that well
matched.
I won't name the vendor (yet) as they are not in production and I'll
see if they bring out a 6 wire power interface for the LEDs. Gotta give
them a chance to rectify it.
I found it amusing that such a basic piece of design was implemented so
crappily.
Cheers
PeteS [posting via google for a few days]
Adrian Jansen
... snip ...
Interesting how simple design stuff gets missed in the rush to get to
market.
But seriously, I would be interested in more details. We are on the
lookout for this type of display for instruments readable in full
sunlight, and none of the CCFL units are good enough.
--
Regards,
Adrian Jansen adrianjansen at internode dot on dot net
Design Engineer J & K Micro Systems
Microcomputer solutions for industrial control
Note reply address is invalid, convert address above to machine form.
PeteS
Well, the CCFL unit we currently use is popular because it is readable
in full sunlight (but that's UK sunlight ;)
What output (lumens) do the ones you have looked at advertise?
One thing about white LED; the output is lower than CCFL generally, but
they are just as readable because the emitted spectra is white, not
somewhat blue.
Once I get back to my real news account (tomorrow night) I'll give
details of highly visible CCFL (provided you aren't in direct
competition with me ;)
Cheers
PeteS
Genome
"Adrian Jansen" <adr...@qq.vv.net> wrote in message
news:12mk1le...@corp.supernews.com...
I was trying to follow your instructions....
Is that
?
I consider myself to be quite intelligent but it took me a bit of time to
work it out so maybe I am not.
Thanks
DNA
Michael A. Terrell
>
> I won't name the vendor (yet) as they are not in production and I'll
> see if they bring out a 6 wire power interface for the LEDs. Gotta give
> them a chance to rectify it.
Why six wire, instead of four wire?
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
Robert Baer
If your country has a government "Adult Protection" group, *WATCH
OUT* that you do not get charged with felony abuse; eg: you threw her
down the staircase that is not in the house, you beat her.
In otherwords, you are guilty without any choice of even knowing the
charges until they toss you into jail!
This shit happens here in the US (in every State) nevermind it it
totally against the Constitution.
Nurses, doctors, "aids" that you pay come in to help with her care
all have a vested interest to "rat" especially if one of them sees a way
to gain (gets an idea you are rich and lets the State take over the
assets that they control, political gain, etc); they support each other.
It snowballs; 5 "aids" helping at different times sees the same
thing, reports the one "problem" and it is a serial offense multiplied
by five.
I have been pushed against that wall, so BE WARNED!
PeteS
> PeteS wrote:
>
> >
> > I won't name the vendor (yet) as they are not in production and I'll
> > see if they bring out a 6 wire power interface for the LEDs. Gotta give
> > them a chance to rectify it.
>
>
> Why six wire, instead of four wire?
Most (not all, of course) regulators designed for LED backlights sense
on the low side, post cathode. In that case, I need each separate
cathode path for sense and each separate anode path for drive as the
voltages across the strings will be different (not by much, but they
will be).
Cheers
PeteS
Tim Shoppa
> This, of course, can easily lead to current hogging above hotspots, and
> did so *even on their own demo unit*. One end of the display was
> noticeably brighter than the rest of the screen, probably because the
> processor and/or power supply for the unit sits in that area. One might
> have expected their on demo unit to be 'tweaked' for such things, at
> least. The rep went quite pink when I opinted it out ;)
>
> I explained to the rep that the best way is to bring out all 3 series
> power separately (as Kyocera does) so they can all be separately
> regulated to ensure equal current (and therefore equal light) from each
> chain. Of course, with each string being separately powered (A and K)
> it's pretty simple to do balancing if the strings aren't that well
> matched.
>
> I won't name the vendor (yet) as they are not in production and I'll
> see if they bring out a 6 wire power interface for the LEDs. Gotta give
> them a chance to rectify it.
Lowest bidder syndrome. Factor in your time and effort in teaching them
how to correctly do what they claim to do and it might not be so cheap
:-).
Not that more expensive bidders never suffer from the same problem!
Tim.
Adrian Jansen
... snip ...
>
> I consider myself to be quite intelligent but it took me a bit of time to
> work it out so maybe I am not.
>
> Thanks
>
> DNA
>
>
Adrian Jansen
visibility such that the display can be read at a glance, with the sun
at any angle. The best units I have seen are used in marine apps, eg
fishfinders, but I havent found a source of the LCDs they use yet.
I have looked at units advertised as 600-700 nits, and in full
Australian sunlight the colors wash out almost completely. The
remaining image in monochrome is readable, but only just, and nowhere
near what an ordinary dot matrix mono transflective LCD can do.
PeteS
I am looking at (and probably going to use) a Kyocera panel. I'll have
to wait until tomorrow at work to get the precise part number. This is
5.7", QVGA, but they do other sizes and resolutions.
I was personally impressed with the readability in full on light, but
the best way is to get a sample and look at it yourself, of course. Do
you have a Kyocera rep. in your black book?
Cheers
PeteS
Adrian Jansen
>
> I am looking at (and probably going to use) a Kyocera panel. I'll have
> to wait until tomorrow at work to get the precise part number. This is
> 5.7", QVGA, but they do other sizes and resolutions.
>
> I was personally impressed with the readability in full on light, but
> the best way is to get a sample and look at it yourself, of course. Do
> you have a Kyocera rep. in your black book?
>
> Cheers
>
> PeteS
Thanks for that. I looked at the Kyocera panels, but the max advertised
brightness is still only 300 nits, which I know is not enough.
PeteS
> PeteS wrote:
>
>>
>> I am looking at (and probably going to use) a Kyocera panel. I'll have
>> to wait until tomorrow at work to get the precise part number. This is
>> 5.7", QVGA, but they do other sizes and resolutions.
>>
>> I was personally impressed with the readability in full on light, but
>> the best way is to get a sample and look at it yourself, of course. Do
>> you have a Kyocera rep. in your black book?
>>
>> Cheers
>>
>> PeteS
>
> Thanks for that. I looked at the Kyocera panels, but the max advertised
> brightness is still only 300 nits, which I know is not enough.
>
I have a close acquaintance who deals with avionics (cockpit) equipment
and the associated panels. I'll drop him a line and ask, but I can't
guarantee anything, obviously.
Cheers
PeteS
PeteS
> PeteS wrote:
>
>>
>> I am looking at (and probably going to use) a Kyocera panel. I'll have
>> to wait until tomorrow at work to get the precise part number. This is
>> 5.7", QVGA, but they do other sizes and resolutions.
>>
>> I was personally impressed with the readability in full on light, but
>> the best way is to get a sample and look at it yourself, of course. Do
>> you have a Kyocera rep. in your black book?
>>
>> Cheers
>>
>> PeteS
>
> Thanks for that. I looked at the Kyocera panels, but the max advertised
> brightness is still only 300 nits, which I know is not enough.
>
Here's the response of the guy I used to work with:
******************************************
All the LCD panels I worked on (that were in production) used
flourescent backlighting.
The backlighting was adjustable with a rotary knob.
flourescents were used as they were the best option at the time.
we did some experiments with leds.
white leds are now the better solution. they should be bright enough
(the leds at least).
they are also more reliable and don't require a high voltage supply.
i remember the only issue i had was matching the white led dimming
curves to the old school flourescent and incandescent.
i seem to remember that there were no COTS solutions for LED backlights
that were acceptable for avionics.
it is necessary to design your own to get the brightness and uniformity
that is required.
these guys make the brightest, i think... http://www.lumex.com/
i saw an article reciently that a new white led was just as bright and
energy efficient as a flourescent.
it is essential to have a anti-glare coatings on the glass and a
mechanical glare shield otherwise the glare will make any display
useless.
organic LED displays will be an excellent choice as a LCD replacement
when the technology stabilizes and manufacturing can maintain the same
panel for at least a few years.
*************************************************
Cheers
PeteS
Didi
while talking displays - today I heard on the BBC Worldservice about
some $100 laptop project at MIT (easy to lookup). They claim to
have achieved so far something like $140; the display they use is
an SVGA... I wonder where do they find those apparently sub-$100
SVGA TFTs so I could go there find one myself. I tend to find them
at $500+ so far...
I found the largest selection of displays - and one which I'll probably
use soon - at Toshiba. How much of those are really to be had and
how much do they cost I don't know, though.
Dimiter
------------------------------------------------------
Dimiter Popoff Transgalactic Instruments
http://www.tgi-sci.com
------------------------------------------------------
PeteS
> Hi Peter,
>
> while talking displays - today I heard on the BBC Worldservice about
> some $100 laptop project at MIT (easy to lookup). They claim to
> have achieved so far something like $140; the display they use is
> an SVGA... I wonder where do they find those apparently sub-$100
> SVGA TFTs so I could go there find one myself. I tend to find them
> at $500+ so far...
> I found the largest selection of displays - and one which I'll probably
> use soon - at Toshiba. How much of those are really to be had and
> how much do they cost I don't know, though.
>
> Dimiter
>
> ------------------------------------------------------
> Dimiter Popoff Transgalactic Instruments
>
> http://www.tgi-sci.com
> ------------------------------------------------------
Maybe it's because the 'standard' sizes are made in such volumes that
they can get that price, but I've yet to find one anywhere close to that.
Cheers
PeteS
Adrian Jansen
Thanks for that, I will follow up.
Michael A. Terrell
>
> Most (not all, of course) regulators designed for LED backlights sense
> on the low side, post cathode. In that case, I need each separate
> cathode path for sense and each separate anode path for drive as the
> voltages across the strings will be different (not by much, but they
> will be).
Thanks. I had to leave the design field when my health failed over
five years ago, and everything in our equipment was CFL tubes.
PeteS
> PeteS wrote:
>> Most (not all, of course) regulators designed for LED backlights sense
>> on the low side, post cathode. In that case, I need each separate
>> cathode path for sense and each separate anode path for drive as the
>> voltages across the strings will be different (not by much, but they
>> will be).
>
>
> Thanks. I had to leave the design field when my health failed over
> five years ago, and everything in our equipment was CFL tubes.
>
The vendor stopped by today with the engineering sample, and sure
enough, just two wires sticking out. He gave the usual '..this is how
everyone does it...' so I showed him my sample from Kyocera (with 6
power leads - 2 for each LED string) and he was rather flummoxed.
I'll test it, but I don't hold out much hope as it's a dense design and
some localised heating is unavoidable.
Cheers
PeteS