jetro57070
LCD?
Joined: 22 Jun 2006
Posts: 1
|
| LCD power supply VO |
 |
|
Why is the LCD voltage different than the logic power supply? The datasheet shows a pot to create VDD-VO at the VO pin on the LCD. is this for contrast? I thought contrast is controlled by software commands.
Also why would you need a pot? datasheet shows VDD-VO to be 0.5v, why not use a voltage divider? or tie them both together? |
Thu Jun 22, 2006 7:56 am |
|
|
Raquel
Matrix Orbital
Joined: 19 Aug 2004
Posts: 645
Location: MO Office |
Hi jetro57070,
Thank you for posting on the forum.
The MOP series does not have software controlled contrast. If you go to our website (www.matrixorbital.com). The Parallel (MOP) series is one of the few series that does not have software controlled contrast.
The pot in the datasheet is suggested so that you may be able to easily have a range of contrast which will suit different lighting conditions.
_________________
Raquel Malinis
Design and Development
Matrix Orbital |
|
Thu Jun 22, 2006 11:30 am |
|
|
AlphaByte
LCD?
Joined: 03 Feb 2009
Posts: 4
|
| Re: LCD power supply VO |
|
|
quote:
Originally posted by jetro57070
Why is the LCD voltage different than the logic power supply? The datasheet shows a pot to create VDD-VO at the VO pin on the LCD. is this for contrast? I thought contrast is controlled by software commands.
Also why would you need a pot? datasheet shows VDD-VO to be 0.5v, why not use a voltage divider? or tie them both together?
Optimal contrast occurs at a very specific voltage. This voltage is beyond
the 5 volt range of the LCD controller. It occurs close to about -7V with
respect to ground. That's about -12V with respect to the 5V rail.
The display module circuit board contains a chip called an inverting voltage
tripler. 5V x -3 = -15V. That -15V is output on pin 20, adjusted by the
divider on the application board, and returned to the display module at V0.
On the display module the V0 is used to generate V1 though V5 for LCD
waveform generation.
In a nutshell, liquid crystal requires more than 5V to polarize. |
|
Fri Jun 04, 2010 4:28 am |
|
|
Clark
Matrix Orbital
Joined: 17 Aug 2007
Posts: 382
|
Hi AlphaByte,
Thanks for the info, it'll provide a great insight for our MOP community.
To clarify your point, our alphanumeric units are usually readable with an LCD supply voltage of around 0v, however, our graphic units will definitely need negative voltage. A negative voltage output will be provided on many of our graphic units, but if need be the info and circuit information you have provided will be a great help.
~Troy
_________________
Troy Clark
Technical Support
Matrix Orbital |
|
Fri Jun 04, 2010 2:19 pm |
|
|
â
 
|
|
All times are GMT - 8 Hours. The time now is Tue Sep 07, 2010 6:08 am
|
|
|
|
| |
SmartFeed
