PLED -- the Holy Grail of display technology?

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We use character LCD displays in many of our apps. Often they are backlit. Sometimes we have used [mostly] compatible VFD.

I found that the PLED "drop-in replacements" for character LCD displays are now available at a decent price from OSD:
http://www.onestopdisplays.net/m...

The current draw looks OK--the 2x20 datasheet has a typical of ~100mW @ 5V.

But there is one disturbing item in the datasheets--shelf life of 5 years, and operating lifetime of ">10k hours".

Now, in an industrial app that is intended to be powered-on 24/7/365 or thereabouts, and there are almost 10k hours in a year, I don't want to be replacing displays left-and-right in a year or two.

Does anyone know if the short lifetime is inherent in this technology? Is there some kind of degrading over time? Should this type of display be avoided for apps that will be always "on"? Has anyone had experience in designing-in PLED character displays? How was the compatibility with HD44780?

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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They sound interesting, but I have to say that I have a lot of big Noritake VFDs
in outdoor industrial apps running 24/7 at max brightness. Some are now over 140,000 hours!
Plant people say they read these things from 100 feet away in broad daylight.

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

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theusch wrote:
How was the compatibility with HD44780?
Lee

The one that I've had a play with from Densitron had an HD44780 compatable controller and it seems to work fine. They really do look good by the way. Amazing viewing angle compared with LCD technology.

I'm also waiting for some OSD1602-B PLEDs to arrive from OSD. It also has an HD44780 controller.

Regarding the 10,000 hours, I've seen other specs which say the 10,000 hours is a half brightness point. So to me it implies the brightness decays with use. Definately a downside to the technology.

Dave.

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I had trouble getting them to work with the standard CVAVR LCD library so I wrote my own code to run them. It is on http://www.cmeter.org/pled/index...
One of the datasheets (attached) I have states a half brightness life over 10,000 hours at room temperature. It also recommends reducing the brightness for extended life. (control voltage 2.5)

Attachment(s): 

Ralph Hilton

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Quote:

Regarding the 10,000 hours, I've seen other specs which say the 10,000 hours is a half brightness point. So to me it implies the brightness decays with use. Definately a downside to the technology.

Thanks for the responses, guys.

--Yes, I like the VFD for the brightness as well. But the cost hit and power draw (and internal heating) are a killer in some apps.

--Do you know if this degradation is per-pixel? Does it matter whether it is lit or not? Where I'm going is trying to find out if it is like "phosphor burn" or not. Then something like moving the "Ready" message around when idle, or some other type of "screen saver" might help.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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The main degradation depends on the brightness.
http://lcd-systeme.com/en/line_b...
Individual LEDs are usually specified with a half brightness lifetime so I would expect moving the ready message to extend life.
http://mctp.chem.ucla.edu/yang/p... gives a somewhat heavy reading explanation.
There is also a deterioration over time which depends on environmental conditions such as moisture and temperature.

Ralph Hilton

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I've had correspondence with OSD on the topic:

--Yes, the lifetime is relatively short but is getting better and better as the technology matures
--Yes, it is on a dot-by-dot basis
--Reducing brightness helps a lot but still doesn't extend lifetime indefinitely

So, it isn't quite ready for 24/7 with indefinite life like LCD or LEDs. But "screen saver" techniques may extend the life to acceptable levels.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Noritake has some LCD replacements that look like these pled things... reverse.. light text on dark bgnd....

Hey Tom P: you sniff the busy on the VFDs? I'm using a 128x32 graphics module... getting some scrambles just using a delay... (maybe one of the delays in the data sheet needs to be longer??)

Imagecraft compiler user

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Thanks Lee, and others, for bringing up this topic. I've been wondering how these PLEDs stack up against the VFDs. Now I'm with Lee on this: not quite ready yet.

Bob, Yes I wait for the busy flag on our VFDs, though I'm not using an SPI interface. I would recommend that you do that instead of fixed length delays. Let us know how it's working out.

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Quote:
Hey Tom P: you sniff the busy on the VFDs? I'm using a 128x32 graphics module... getting some scrambles just using a delay... (maybe one of the delays in the data sheet needs to be longer??)

Hi Bob,
I'm actually just buying the Noritake glass (2x20x11mm) and mounting them on my own board. I use the
Rockwell-type 10938 & 10939 driver chips which have a parallel interface arrangement.
I tried a sample module with a serial interface some years ago. It seemed to work but
I only played with it for an afternoon. I'm pretty sure I just wrote to it "blind". Because
of environmental temp requirements and a desire to not burden my 5 volt supply with the
substantial load the display module wanted(>1A!), I built my own drivers and power supplies.
(I wanted my dc-dc converters to feed off 24 volts)

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

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I should add that the demo code in the datasheet doesn't work - it switches the display off before writing to it. Also it uses floating point loop counters!

Ralph Hilton

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Can someone give a very brief explanation of what "PLED" refers to? I looked on the OSD web site and it wasn't much help.

Thanks
Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Quote:

Noritake has some LCD replacements that look like these pled things... reverse.. light text on dark bgnd....

Yes, and we have used them. Some of the tradeoffs:

--the Noritake VFDs cost roughly twice as much as an equivalent backlit character LCD. That extra US$10/unit can be a killer sometimes. The OSD modules that I looked at had pricing roughtly equivalent to the backlit character LCDs. With the better viewing qualities [than the backlit LCDs, and about the same as the VFD maybe], chalk one up for the PLED.

--the Noritake VFDs consume ~150-200mA. A backlit LCD ~100mA when the backlight is on. The PLED display is ~20mA. Chalk up another for the PLED, both power supply requirements and heat dissipation.

--VFD & PLED will be better at low temperatures than LCD. [High temps are about a wash???]

Given the above, the short lifetime of the PLED may be a killer factor. Otherwise, they seem to stack up well.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Quote:

I looked on the OSD web site and it wasn't much help.

Didja try this:
http://www.onestopdisplays.net/F...

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Polymer Organic LED displays are nice.
At 5 years, looks like 10.000 write times of flash, it's only guaranteed lifetime.
I cannot believe after 6 years you cannot see an image on the display?
VFD last long, about 15-25 years.
But PLED is very fast (10ns), how fast is VFD?

:?

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Thanks, Lee!

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!