EEVblog #1044 - LCD Technology Tutorial

[EEVblog]

Part 1 in a series of videos on designing a custom LCD display.
This tutorial covers how LCD displays work, the 3 different types of interface (DIP, Elastomeric, Flex), the three different optical types (Reflective, Transflective, and Transmissive), and the two different types of drive (Static vs Dynamic)
Microchip  AN658
http://ww1.microchip.com/downloads/en/AppNotes/00000658B.pdf

[floobydust]

Link "video unavailable" fixed 
Please include low temperature fluids, use them here in the Great White North down to -30C. Needs more drive though, +/-5V and contrast moves around lots with temperature.

[tautech]

Looking forward to the future vids, excellent topic. 

[W2NAP]

hmmm "This video is unavailable."

something is broken. 

[rs20]

I think he's correcting a couple of issues; which is awesome -- trading in short-term view stats in order to ensure that he has an awesome, accurate video in perpetuity.

[EEVblog]

New upload link working again.

[SeanB]

Is there going to be a video about driving an LCD display with multi bias voltage levels?

He does mention a few times the next one about LCD will cover that.

[unclebob]

Really great tutorial, I can't wait to see the other parts. Thanks a lot.

[EEVblog]

Is there going to be a video about driving an LCD display with multi bias voltage levels?

I don't think that far ahead.

[jonovid]

Thanks Dave.it's about time! looking forward to next video. 
what happened when posting the video to YouTube. 
some of us like to fiddle or mod LCD displays for fun. 

[Twoflower]

Very informative as usual  .

But the term "LCD Display" makes me shudder all the time. It's just not a Liquid Crystal Display Display. But as a non native English speaker I should be careful for what I call for

[richnormand]

Nice video Dave. Looking forward to the next one.

Suggestions for followup videos (in addition to added tutorials)

Looking at:
Driving schemes and pitfalls for directly addressed LCDs with standard chips.
Are there standard pinouts/voltages to look for?
Embedded/onboard hardware and software drivers with LCDs to look for (like the Noikia with ARM Cortex drivers combo (Github)

Also of importance for many that have older equipment:
Any way to increase the contrast of LCD panels on older HP, Ithaco, Pace, Canberra and the like. Typically they do not have contrast adjustments and are only readable using a strong light in front of the display now .
Any way to regenerate the older LCD to work better, as many of these displays are OEM and not replacable.

Options for adding back lighting to LCDs that did not have provision for that (like some of the retrofits shown on the EEVblog forum)

Keep up the good work.

Cheers and thanks.

[Ertew]

Dave, can You include "silver polarizer" and frontlight in next videos?
 
Transflective LCD have "black polarizer" on both sides and reflector on bottom. Light that doesn't pass are absorbed by polarizer. Silver polarizer (located at bottom of LCD instead of black polarizer and reflector) reflect light that doesn't pass through. In this construction active segments shows light from backlight unit while inactive segments shows light from environment. Results: poor contrast in poor light but excellent both in sunlight and darkness.

Second nice technology are reflective display + frontlight unit. Technology was popular years ago when other types cannot give enough brightness. Photos below shows my ST5111 (reflective) and E52 (transflective). Both with light turned off.

http://forum.bongofish.co.uk/index.php?topic=2561.0 - here are my review of that ST5111 tablet-PC. Sadly all photos are gone.

Any way to regenerate the older LCD to work better, as many of these displays are OEM and not replacable.

Broken LCD cannot be fixed. But broken connectors (common problem) can be easy to fix by replacing zebra rubber or carbon flat flex cable. The most problematic damage are broken conductive tracks on LCD.

[Mr. Scram]

I noticed a while back that ultra cheap items, like a 4 dollar multimeter and a calculator, often had very nice high contrast displays even when compared to very expensive multimeters. I wondered about that and I guess this video explains it. No backlight!

[HKJ]

I noticed a while back that ultra cheap items, like a 4 dollar multimeter and a calculator, often had very nice high contrast displays even when compared to very expensive multimeters. I wondered about that and I guess this video explains it. No backlight!

There is also another explanation: Simple display. Simple multiplexing gives better contrast.

[Peabody]

This discussion brings to mind the fact that the display on my Sharp Carousel microwave oven is getting dimmer with age.  It appears this is a common problem on a lot of such ovens.  Everything still works fine, but you just can't quite read the display anymore.  An odd form of planned obsolescence.

But on closer inspection, the segments are actually lit up, on a black background.  Does that mean it's really an LED display, not LCD?  Well, I guess the backlight could be amber.  There is a bit of polarizer darkening, but not total like my laptop display.  The Youtube videos on this problem refer to Sharp LCD display.  So is it likely there is a fix - short of replacement?

[EEVblog]

I noticed a while back that ultra cheap items, like a 4 dollar multimeter and a calculator, often had very nice high contrast displays even when compared to very expensive multimeters. I wondered about that and I guess this video explains it. No backlight!

All things being equal, less or no multiplexing = better contrast.
More expensive meters typically have dual display, bargraph etc, that means a lot more segments, more commons, and more multiplexing required.

[coppice]

This discussion brings to mind the fact that the display on my Sharp Carousel microwave oven is getting dimmer with age.  It appears this is a common problem on a lot of such ovens.  Everything still works fine, but you just can't quite read the display anymore.  An odd form of planned obsolescence.

But on closer inspection, the segments are actually lit up, on a black background.  Does that mean it's really an LED display, not LCD?  Well, I guess the backlight could be amber.  There is a bit of polarizer darkening, but not total like my laptop display.  The Youtube videos on this problem refer to Sharp LCD display.  So is it likely there is a fix - short of replacement?

Most older microwave ovens, and even many new ones, use VFDs (Vacuum Flourescent Displays). Like any form of electron tube they do wear with age, and become dimmer. Their lives aren't too bad, though. If you've had the oven 10 years, and its one which displays the time all day long, the display has run for nearly 100k hours. That's not a bad life for a low cost electron gun device.

[coppice]

All things being equal, less or no multiplexing = better contrast.
More expensive meters typically have dual display, bargraph etc, that means a lot more segments, more commons, and more multiplexing required.

History has been largely as you said. 1mux being higher contrast, wider viewing angle and wider temperature range that 2mux, with this pattern going up to 4mux. However, for displays beyond 160 segments (40x4) its getting common to use 6mux or 8mux. Many of these give really good contrast over a wide viewing angle and a reasonable temperature range while running from just 3 volts. To get most 4mux displays to work well over a wide temperature range you need nearer to 4 volts. I don't know what is different about the design of these higher mux panels.

[Peabody]

Most older microwave ovens, and even many new ones, use VFDs (Vacuum Flourescent Displays). Like any form of electron tube they do wear with age, and become dimmer. Their lives aren't too bad, though. If you've had the oven 10 years, and its one which displays the time all day long, the display has run for nearly 100k hours. That's not a bad life for a low cost electron gun device.

It's a Sharp R-303CW, and I found the manual and schematic for it.  It is an LCD display, and appears to have an LED backlight - four LED's in series with an 82-ohm resistor to ground, controlled by one PNP transistor.

The display has 25 pins, composed of 22 SEG and 3 COM.  There's a big ribbon connector, but I think if that was the problem there would be some segments dimmer than others, or completely dark.  But mine is just uniformly dim.  So, it's a mystery.

Built in 2001.  Hell, it's barely broken in.

[Mr. Scram]

All things being equal, less or no multiplexing = better contrast.
More expensive meters typically have dual display, bargraph etc, that means a lot more segments, more commons, and more multiplexing required.

In this case it's a calculator with a graphic display, so I assume it does lots of multiplexing. Not too long ago this calculator would have been the duck's guts, now it's about as cheap as they come. In the case of the multimeter you're probably right, though!

[Mr. Scram]

This discussion brings to mind the fact that the display on my Sharp Carousel microwave oven is getting dimmer with age.  It appears this is a common problem on a lot of such ovens.  Everything still works fine, but you just can't quite read the display anymore.  An odd form of planned obsolescence.

But on closer inspection, the segments are actually lit up, on a black background.  Does that mean it's really an LED display, not LCD?  Well, I guess the backlight could be amber.  There is a bit of polarizer darkening, but not total like my laptop display.  The Youtube videos on this problem refer to Sharp LCD display.  So is it likely there is a fix - short of replacement?

As a side note, I've noticed how people have shifted towards calling a lot of forms of wear or weaknesses in a design "planned obsolescence". In my mind there has to be a very intentional and deliberate act of shortening the lifespan of a product by the design choices made to call it that. Something that's run for over 15 years continuously and still works can, in my mind, not be called planned obsolescence by definition.

[rs20]

As a side note, I've noticed how people have shifted towards calling a lot of forms of wear or weaknesses in a design "planned obsolescence". In my minds there has to be a very intentional and deliberate act of shortening the lifespan of a product by the design choices made to call it that. Something that's run for over 15 years continuously and still works can, in my mind, not be called planned obsolescence by definition.

+1. I think they're just trying to be "edgy" and "stick it to the man".

[ggchab]

Very interesting tutorial  Thanks

[Peabody]

As a side note, I've noticed how people have shifted towards calling a lot of forms of wear or weaknesses in a design "planned obsolescence". In my minds there has to be a very intentional and deliberate act of shortening the lifespan of a product by the design choices made to call it that. Something that's run for over 15 years continuously and still works can, in my mind, not be called planned obsolescence by definition.

+1. I think they're just trying to be "edgy" and "stick it to the man".

Ok, I'll admit to being unfair about that.  It just seemed a shame that something still working perfectly would have to be replaced just because the display is getting too dim to see.  I'm still curious about why it's dim.  Segments that have been turned on only a few times in that 15 years are dim too, like the "defrost" indicator.  Well I'll go back and view the episode again and see what might apply.