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'[OT]LCD experiment part 2'
1998\12\08@180158 by Bob Blick

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Even with the polarizer rotated for best performance at the viewing angle
I wanted it was still not as good as the intended angle.

I decided to mess with the rear polarizer. I still could not get the
result I wanted.

My resulting conclusion is that it's impossible to change the intended
viewing angle of an LCD display, unless you can rotate both polarizers by
some angle that isn't 180 or 90.

-Bob

1998\12\08@213503 by Reginald Neale

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>Even with the polarizer rotated for best performance at the viewing angle
>I wanted it was still not as good as the intended angle.
>
>I decided to mess with the rear polarizer. I still could not get the
>result I wanted.
>
>My resulting conclusion is that it's impossible to change the intended
>viewing angle of an LCD display, unless you can rotate both polarizers by
>some angle that isn't 180 or 90.
>
Bob:

I'd order some polarizing film from Edmund Scientific and change them both
at once. At least you'd have big enough pieces to do some decent
experiments with.

Reg Neale

1998\12\08@224941 by Sean Breheny

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Hi Bob,

At 02:49 PM 12/8/98 -0800, you wrote:
>Even with the polarizer rotated for best performance at the viewing angle
>I wanted it was still not as good as the intended angle.
>
>I decided to mess with the rear polarizer. I still could not get the
>result I wanted.
>
>My resulting conclusion is that it's impossible to change the intended
>viewing angle of an LCD display, unless you can rotate both polarizers by
>some angle that isn't 180 or 90.

And before, you also wrote:

>Rotating 90 degrees does exactly what I need. I suppose I could cut the
>polarizer into 10 little pieces and reassemble them to get this effect on
>the whole display.

The fact that flipping the front one over (sticky side out) has ANY affect,
seems to me to suggest that it is not a linear polarizer(these work the
same way in either direction).  The only setup that I have seen cause this
behavior was a laminate of a linear polarizer and a birefringent plate
(causes components of the E field of polarized light along one axis to be
phase shifted relative to the other axis).

I just did a search for how LCDs work and got,among others, the following URL:

http://www.angleview.com/lcdwork/index.htm

Looking at this page and several others, it seems that only linear
polarizers should be involved in your LCD, and why they should be working
differently in one direction than in the other, I can't understand. It
would also seem to me that rotating 135 deg should invert the display
(normally black instead of normally white), and that rotating 90 deg should
make the thing not work at all (always white,since this would allign the
front and back polarizers).

I don't really understand the reason why the lcd has a specific viewing
angle. The only thing I can think of would be that the ability of the LC's
to twist the polarization of the light going thru them is dependent upon
the angle at which the light is hitting them. If this were true, I don't
think you could do anything with the two polarizers to make it work at a
different angle because the light going through would be unaffected by the
state of the voltage across the LC electrodes.

Then again, the pages I looked at might only have info on one type of
display, and there may be others which work very differently.

Hope this rather lame attempt helps somewhat!

BTW, I would be interested in what you find out in the end.

Sean


+-------------------------------+
| Sean Breheny                  |
| Amateur Radio Callsign: KA3YXM|
| Electrical Engineering Student|
+-------------------------------+
Save lives, please look at http://www.all.org
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1998\12\08@235824 by Vance Gloster

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-----Original Message-----
From: Sean Breheny <.....shb7KILLspamspam@spam@CORNELL.EDU>
>Looking at this page and several others, it seems that only linear
>polarizers should be involved in your LCD, and why they should be working
>differently in one direction than in the other, I can't understand. It
>would also seem to me that rotating 135 deg should invert the display
>(normally black instead of normally white), and that rotating 90 deg
should
>make the thing not work at all (always white,since this would align the
>front and back polarizers).

Actually here is how it works.  Assume it is backlit (just to make it
easier to imagine).  The back polarizing filter takes the light and
polarizes it, say, horizontally.  The active elements in the crystal rotate
the polarization by 90 degrees (not exactly, but close enough for a thought
experiment), making the light traveling through the active elements
polarized vertically.  Then we get to the front polarizing filter, which is
polarized horizontally.  It lets the light shine through at the points
where the light is polarized horizontally, making the active elements
appear black (because the light passing through them is polarized
vertically and is blocked by the filter).

A non-backlit works exactly the same way except the light passes from front
to back and is reflected passing from back to front.  Two trips do the same
thing that one trip does.

Lets go back to the backlit case.  If the front filter is polarized
vertically (rotated 90 degrees), it allows *vertically* polarized light to
pass through, making the active elements appear "lit", and it blocks the
horizontally polarized light, making the rest appear black.

Rotating the filters to a different polarization angle should have little,
if any, effect on the viewing angle.  But the reversed display may be
easier to read at a poor viewing angle.

Vance Gloster            When a truth becomes a fact it loses all
vancespamKILLspameni.net                    intellectual value. -Oscar Wilde

1998\12\09@015929 by Sean Breheny

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Hi Vance,

What you say makes sense, but it doesn't jive with the diagrams at the URL
I posted. In that page, it appears to show the two polarizers being
crossed, and the LCs causing a 45 deg rotation.

Also, much more importantly, I still don't understnad why
flipping(reversing front to back) a linear polarizer over should EVER make
a difference, as Bob indicated it was in his case.

Thanks,

Sean

At 08:44 PM 12/8/98 -0800, you wrote:
>Actually here is how it works.  Assume it is backlit (just to make it

+-------------------------------+
| Sean Breheny                  |
| Amateur Radio Callsign: KA3YXM|
| Electrical Engineering Student|
+-------------------------------+
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
.....shb7KILLspamspam.....cornell.edu  Phone(USA): (607) 253-0315 ICQ #: 3329174

1998\12\09@102239 by Reginald Neale

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I think the sheet polarizer materials have the molecules of polarizing
material  all uniformly aligned and nicely straightened. One can speculate
that the pasty gunk inside the LCD is not as well behaved; that could
explain why it looks different from one direction than from another.

(I'm not a materials scientist; I only play one on the Internet. :-))

Also, in an earlier similar discussion it was suggested that if you have
access to segment-level control of the LCD, you could transform a 6:00
device into a 12:00 one by inverting segment addressing from top/bottom and
right/left and then viewing it upside down.

Reg Neale

1998\12\09@113132 by Peter L. Peres

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On Wed, 9 Dec 1998, Sean Breheny wrote:

> Also, much more importantly, I still don't understnad why
> flipping(reversing front to back) a linear polarizer over should EVER make
> a difference, as Bob indicated it was in his case.

The polarization direction on polarizers need not follow an axis of the
physical device. If it is 45 degres and you flip it it becomes -45 degrees
and inverts the display luminance. q.e.d.

Peter

1998\12\09@114338 by Bob Blick

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> Also, much more importantly, I still don't understnad why
> flipping(reversing front to back) a linear polarizer over should EVER make
> a difference, as Bob indicated it was in his case.

Looking at the polarizer through a pair of Polaroid sunglasses, it appears
the polarizer is at a 45 degree angle, so flipping it upside down has the
effect of reversing the action.

I've made quite a mess of this LCD, but I might as well learn as much
about it as I can.

I had considered using the whole thing upside down, using a combination of
the 8 ram-based characters and also characters that are symmetrical, but
it seemed pretty wacky.

A thing I did try was to flip the LCD around on the PC board. It works,
but the display is a "5 x 7 with underline cursor" and when I flipped it
there was a gap between the upper(formerly underline) row of pixels and
the rest of the pixels. This did give me something to think about. I might
buy a large character display with 5 x 8 pixel array and try the same
thing(though I think I was very lucky to have an LCD with symmetrical
electrical layout).

-Bob

1998\12\09@114344 by Sean Breheny

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Hi Peter,

At 06:10 PM 12/9/98 +0000, you wrote:
>The polarization direction on polarizers need not follow an axis of the
>physical device. If it is 45 degres and you flip it it becomes -45 degrees
>and inverts the display luminance. q.e.d.

Of course, you are right. I don't know why I didn't think of that case. In
fact, if it is at 45 deg, flipping it over is the same as rotating it by 90
deg.

Thanks,

Sean

+-------------------------------+
| Sean Breheny                  |
| Amateur Radio Callsign: KA3YXM|
| Electrical Engineering Student|
+-------------------------------+
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
EraseMEshb7spam_OUTspamTakeThisOuTcornell.edu  Phone(USA): (607) 253-0315 ICQ #: 3329174

1998\12\09@131858 by Marc

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> I decided to mess with the rear polarizer. I still could not get the
> result I wanted.

You can use a 6 o'clock _graphics_ display and mount it 180¡ vice-versa.

The P120-5N for example has 120x32 pixels, comparable to 20x4 characters
on those HD44something displays. It contains 2x SED1520 controller.

By defining the font in your micro upside down, you can compensate for
the wrong mounting orientation.

The particular display I mentioned costs about $25 in small quantities
here, and has LED backlight. For the 8515 I have done a driver (in C)
that supports multiple proportional fonts of up to full screen size,
typefaces bold & ghosted, as well as printing of pixel-exact rectangular
crops from the ASCII input string (for scrolling support). I won't give
that out for free though..

1998\12\09@153852 by John Payson

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|A thing I did try was to flip the LCD around on the PC board. It works,
|but the display is a "5 x 7 with underline cursor" and when I flipped it
|there was a gap between the upper(formerly underline) row of pixels and
|the rest of the pixels. This did give me something to think about. I might
|buy a large character display with 5 x 8 pixel array and try the same
|thing(though I think I was very lucky to have an LCD with symmetrical
|electrical layout).

I would not be at all surprised if a significant percentage of the
ubiquitous alphanumeric displays on the market have a layout which
is electrically symetrical.  If such a display also has a uniform
8-dot high character matrix (instead of 7+gap+cursor) it probably
could be flipped 180 degrees with the effect of changing the viewing
angle and 'nothing else'.

Alternatively, though I've not tried programming it, the 32x4 display
from Timeline ($10) uses a different controller scheme from the norm
and allows all 128 characters to be assigned their own shapes.  Unfor-
tunately, it has gaps between the characters (so it's not a full graph-
ics display) and it requires even more pins to interface than the typical
Hitachi (though a small amount of glue would help considerably).


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1998\12\09@193050 by brad

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John Payson wrote:
>
> |A thing I did try was to flip the LCD around on the PC board. It works,

>                   Name: WINMAIL.DAT
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>               Encoding: x-uuencode

Hi John,
Just in case nobody has mentioned it. It's Baaaaaaaaaaack!
Man I hate Outlook :p)

Cheers

--
-----------------------------------
Brad Campbell
Technical Manager

Seme Electrical Engineering Co
59 Collingwood St Osborne Park 6017
Western Australia
Ph    :-+61 8 9445 2577
Fax   :-+61 8 9244 1327
Email :- bradspamspam_OUTseme.com.au

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1998\12\10@061308 by John Sanderson

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Hello John & PIC.ers,  -and-whoever-started-this-
..
>Date:    Wed, 9 Dec 1998 14:39:18 -0600
>From:    John Payson <@spam@supercatKILLspamspamCIRCAD.COM>
>
>|A thing I did try was to flip the LCD around on the PC board. It works,
>|but the display is a "5 x 7 with underline cursor" and when I flipped it
<snip>
>
>I would not be at all surprised if a significant percentage of the
>ubiquitous alphanumeric displays on the market have a layout which
>is electrically symetrical.  If such a display also has a uniform
..
I thought exactly the same a month or two ago, and tried it with
Optrex, Rohm & an old Philips alphanumeric display.
I was surprised to find it wouldn't work with any of them, the
glass-edge connectors hadn't been made with 180 deg symmetry in mind.
..
As I still have an interest in solving this, I'd like to hear from
anyone who's actually done this & got it right (what manufacturer? etc)
..
Vendors here only stock whatever moves in quantity
(is it different elsewhere?), which means I can't get 12 o'clock
displays off-the-shelf.
El-neato if there's a 6 o'clock one I can get ex stock, which can be
gippoed this way.
..
Best regards,   John
..
email from John Sanderson at
JS Controls, PO Box 1887, Boksburg 1460, Rep. South Africa
Manufacturer & purveyor of laboratory force testing apparatus
and related products and services.
Tel/fax: Johannesburg 893 4154    Cellphone 082 453 4815

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