Forums

OT: LCD BIAS understanding

Started by Unknown June 22, 2005
Hi all,

 

Can anyone explain me what bias means on an lcd module?

As far as I understand it it has something to do with the LCD contrast, but
if that the case than it would not matter how I drive the lcd , 1/3 bias or
what ever. Unfortunate this is not trough, why??

 

Ive written a small test programm and had a lot of looks through sample
code on driving LCDs using the MSP430F413 or any other. But all of them are
build for normal mode lcd ie 2MUX =>  bias; 3mux, 1/3 bias etc but non was
written for 3mus,  bias (an lcd I found works this way)

 

So I thought okay lets test some but non of them gave me anything I
expected.

By now I changed display and all is well, but still I dont understand th
bias thing.

 

Could anyone help me out??

 

 

thanks martijn

 






Beginning Microcontrollers with the MSP430

Damn! I just typed a reply, then somehow XP ate it!

OK, I've waited to reply since I'm not an LCD expert, but nobody else 
has chimed in so I will.

LCD crystals require a AC drive signal, DC would kill them. This is 
derived from two waveforms, COMMON and SEGMENT. These waveforms are 
switched DC levels, typically derived from a signal called Vo on 
character and graphics panels. This voltage level is usually subdivided, 
typically into 4 or more levels (six and 7 levels are common). The 
differential voltage supplied to a single crystal determines whether it 
is on or off, there being a fair amount of hysteresis in between. The 
crystals are somewhat persistent, once darkened they take some time to 
fade back to clear, thus to maintain a dark state each crystal must be 
activated at a rate faster than their decay rate. This is determined by 
the frame, line and dot clocks. Contrast is therefore a function of 
differential voltage level and time between pixel updates. Changing the 
clock, or altering the frame clock will require Vo to be adjusted.

The drive signal, as seen by each pixel, must change phase on alternate 
updates, to maintain the apparent AC drive.

For a more complete view download a tech manual, such as g321ev. pdf 
from an Lcd manufaturer such as Seiko.

Al


martijnbroens@mart... wrote:

>Hi all,
>
> 
>
>Can anyone explain me what bias means on an lcd module?
>
>As far as I understand it it has something to do with the LCD contrast, but
>if that the case than it would not matter how I drive the lcd , 1/3 bias or
>what ever. Unfortunate this is not trough, why??
>
> 
>
>Ive written a small test programm and had a lot of looks through sample
>code on driving LCDs using the MSP430F413 or any other. But all of them are
>build for normal mode lcd ie 2MUX =>  bias; 3mux, 1/3 bias etc but non
was
>written for 3mus,  bias (an lcd I found works this way)
>
> 
>
>So I thought okay lets test some but non of them gave me anything I
>expected.
>
>By now I changed display and all is well, but still I dont understand th
>bias thing.
>
> 
>
>Could anyone help me out??
>
> 
>
> 
>
>thanks martijn
>
> 
>
>
>
>
>
>
>
>.
>
> 
>Yahoo! Groups Links
>
>
>
> 
>
>
>
>
>  
>


On Tue, 12 Jul 2005 23:07:51 +0930, Al wrote:

><snip>
>For a more complete view download a tech manual, such as g321ev. pdf 
>from an Lcd manufaturer such as Seiko.

Do you have a working link?  I'm interested in reading a detailed
description.

(Just used google without much success -- no, I will not screw around
with alldatasheet.com to even find out.)

Thanks,
Jon

Hi,

http://www.google.com/search?q=g321ev.pdf

Regards,

Rolf

msp430@msp4... schrieb am 12.07.05 18:29:29:
> 
> On Tue, 12 Jul 2005 23:07:51 +0930, Al wrote:
> 
> ><snip>
> >For a more complete view download a tech manual, such as g321ev. pdf 
> >from an Lcd manufaturer such as Seiko.
> 
> Do you have a working link?  I'm interested in reading a detailed
> description.
> 
> (Just used google without much success -- no, I will not screw around
> with alldatasheet.com to even find out.)
> 
> Thanks,
> Jon
> 
> 
> .
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 
> 



On Tue, 12 Jul 2005 19:06:17 +0200, you wrote:

>Hi,
>
>http://www.google.com/search?q=g321ev.pdf
>
>Regards,

I did that and checked the links.  nada.

Jon

http://www.tiking.com/compment.asp?compment=SII\G321EV.pdf55555555G3

click in the first button 


-----Original Message-----
From: msp430@msp4... [mailto:msp430@msp4...] On Behalf Of
Jonathan Kirwan
Sent: Tuesday, July 12, 2005 3:18 PM
To: msp430@msp4...
Subject: Re: [msp430] OT: LCD BIAS understanding


On Tue, 12 Jul 2005 19:06:17 +0200, you wrote:

>Hi,
>
>http://www.google.com/search?q=g321ev.pdf
>
>Regards,

I did that and checked the links.  nada.

Jon


.

 
Yahoo! Groups Links



 



-- 
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.323 / Virus Database: 267.8.12/46 - Release Date: 11/7/2005
 


On Tue, 12 Jul 2005 15:51:44 -0300, augusto wrote:

>http://www.tiking.com/compment.asp?compment=SII\G321EV.pdf55555555G3
>
>click in the first button 

I clicked on a number of buttons there.  At first, I had no luck.
Here is one of the pages it took me to, that looked interesting
though:

  http://www.tiking.com/fenlei.asp?lei=G3

One of the links takes me to an error page, namely:

  http://www.tiking.com/error.asp

But after thinking about this, I realized that it is probably because
I have my security set rather high and I don't permit cookies from
anyone other than specific sites I permit, when I care to do so.  So I
changed this, and that seemed to make it work.

Thanks,
Jon

I've just uploaded this to the files area, since a few people seem 
interested.

Al

Jonathan Kirwan wrote:

>On Tue, 12 Jul 2005 23:07:51 +0930, Al wrote:
>
>  
>
>><snip>
>>For a more complete view download a tech manual, such as g321ev. pdf 
>>    
>>
>>from an Lcd manufaturer such as Seiko.
>
>Do you have a working link?  I'm interested in reading a detailed
>description.
>
>(Just used google without much success -- no, I will not screw around
>with alldatasheet.com to even find out.)
>
>Thanks,
>Jon
>
>
>.
>
> 
>Yahoo! Groups Links
>
>
>
> 
>
>
>
>
>
>  
>


>LCD crystals require a AC drive signal, DC would kill them.

Really?  What do you mean "kill them"?  I would think an improper DC
bias 
MIGHT make the segments non-viewable, but not destroy the LCD.

Lou



Well according to some texts I have it will destroy the crystals,  which 
is a reasonable interpretation of making the pixels non viewable I 
guess. hey, I didn't profess to be an expert.

Al

Lou C wrote:

>>LCD crystals require a AC drive signal, DC
would kill them.
>>    
>>
>
>Really?  What do you mean "kill them"?  I would think an improper
DC bias 
>MIGHT make the segments non-viewable, but not destroy the LCD.
>
>Lou
>
>
>
>
>.
>
> 
>Yahoo! Groups Links
>
>
>
> 
>
>
>
>
>  
>