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18-02-2010, 09:57 PM
Post: #1
lcd display
hi ,i need to prepare a seminar abt lcd display..
i need information about its working principle,uses,advantages and disadvantages.
It wud be fine if u provide information abt ne other topic(electronic)as well

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16-05-2010, 01:28 PM
Post: #2
RE: lcd display

.ppt  LCD-liquid crystal display.ppt (Size: 4.87 MB / Downloads: 210)

liquid crystal display(LCD)


PRESENTED BY
RAJENDRA KUMAR NATH



WHAT IS LCD

A liquid crystal display(LCD) is an electronically-modulated optical device shaped in to a thin, flat panel made up of a color or monochrome pixels filled with liquid crystals and arrayed in front of light source(backlight) or reflector.

USE OF LCD

LCDs are commonly used for:-
Portable electronic games
Digital cameras and camcorders
Video projection system
Monitors for computers
Flat-panel televisions
Wrist watches
etc


A BRIEF HISTRY

1888:-Friedrich Reinitzer (1858-1927) discovers the liquid crystalline nature of cholesterol extracted from carrots
1904:-Otto Lehmann publishes his work "Liquid Crystals".
1911:-Charles Mauguin describes the structure and properties of liquid crystals.
1962:-Richard Williams found that liquid crystals had some interesting electro-optic characteristics and he realized an electro-optical effect by generating stripe-patterns
1972:-The first active-matrix liquid crystal display panel was produced in the United States by T. Peter Brody.


ADVANTAGE OF LCD

LCDs have great advantage over conventional display
Least power consumption
Can be fabricated in small area
low cost & portable


LIQUID CRYSTAL

Liquid crystal state is a phase of mater which is exhibited by a large no. of organic material over a restricted temperature range.
At the lower end of temperature the material is crystalline solid
At the upper end of temperature it changes into clear liquid
Within this range it has a milky yellowish appearance & combine some of the optical property



Property:-

The major characteristic is rod lik In the present day The nematic & cholestric structure are important in display device
e shape of there molecule
At the liquid crystal stage molecule can take up a certain orientation. This orientation is called


TYPE OF ORDERING OF CRYSTAL

Nematic
Cholestric
Smectic



NEMATIC

Nematic is a Greek word means Thread
In this ordering molecule or directors aligned in parallel to each other.
Molecule are free to move relative to each other hence this phase has liquid property
This liquid crystal behavior can occur at temperature range 20o to 47o centigrade
The molecule usually consist of two benzene ring linked with a central group
Example:-



CHOLESTRIC

It made up from a large no of plane each having nematic like structure.
The director directions thus display a helical twist through the material.
The distance between plane of same director called pitch



ORDERING OF CRYSTAL W.R.T SOLID SURFACE

Homeotropic Ordering:- Perpendicular to the surface of glass
Homogeneous Ordering:- Parallel to the surface of glass
E Homogeneous ordering can be obtain by rubbing the surface once or twice along the particular direction with a soft fabric.
ELiquid crystal molecule take up an orientation parallel to direction of rubbing.



TWISTED NEMATIC CELL

ON STATE:-
¢ Application of 3 to 5 volts across the plate destroys the twisted state and causes the molecules to orient perpendicular to the substrate.
¢ Giving a dark appearance to the cell

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15-10-2010, 09:12 AM
Post: #3
RE: lcd display
LCD Display


More microcontroller devices are using 'smart LCD' displays to output visual information. The following discussion covers the connection of a Hitachi LCD display to a PIC microcontroller. LCD displays designed around Hitachi's LCD HD44780 module, are inexpensive, easy to use, and it is even possible to produce a readout using the 8 x 80 pixels of the display. Hitachi LCD displays have a standard ASCII set of characters plus Japanese, Greek and mathematical symbols. For a 8-bit data bus, the display requires a +5V supply plus 11 I/O lines. For a 4-bit data bus it only requires the supply lines plus seven extra lines. When the LCD display is not enabled, data lines are tri-state which means they are in a state of high impendance (as though they are disconnected) and this means they do not interfere with the operation of the microcontroller when the display is not being addressed.
The LCD also requires 3 "control" lines from the microcontroller.

Enable (E) This line allows access to the display through R/W and RS lines. When this line is low, the LCD is disabled and ignores signals from R/W and RS. When (E) line is high, the LCD checks the state of the two control lines and responds accordingly.

Read/Write (R/W) This line determines the direction of data between the LCD and microcontroller. When it is low, data is written to the LCD. When it is high, data is read from the LCD.

Register select (RS) With the help of this line, the LCD interprets the type of data on data lines. When it is low, an instruction is being written to the LCD. When it is high, a character is being written to the LCD.

Logic status on control lines:

E 0 Access to LCD disabled
1 Access to LCD enabled

R/W 0 Writing data to LCD
1 Reading data from LCD

RS 0 Instruction
1 Character

Writing data to the LCD is done in several steps:

Set R/W bit to low
Set RS bit to logic 0 or 1 (instruction or character)

For more information about this article,please follow the link:
http://www.google.co.in/url?sa=t&source=...OGYtqEKH4A

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01-01-2011, 01:11 PM
Post: #4
RE: lcd display


Parth Patel
Sunil patel



.ppt  LCDppt1.ppt (Size: 975.5 KB / Downloads: 70)

Contents
1.   What’s Liquid Crystals (LC)
2.   Introduction to Liquid Crystal Displays
3.   Operating Principle
4.   Display Addressing
5.   Applications A) Thin Film Transistor (TFT) B) Alpha-numeric Display C) Back Lighting System
6. Reference

1.   What’s Liquid Crystals (LC)
intermediary substance between a liquid and solid state of matter. e.g. soapy water
light passes through liquid crystal changes when it is stimulated by an electrical charge.
Examples of LCs

2.   Introduction to Liquid Crystal Displays
Consists of an array of tiny segments (called pixels) that can be manipulated to present information.
Using polarization of lights to display objects.
Use only ambient light to illuminate the display.
Common wrist watch and pocket calculator to an advanced VGA computer screen

Different types of LCDs
Passive Matrix LCDs (PMLCD) and Active Matrix LCDs (AMLCD)
Passive Twisted Nematic Displays (TNLCD)
Super Twisted nematic LCD (STNLCD)
Thin Film Transistor LCD (TFT LCD)
Reflective LCD
Rear Projection LCD

3. Operating Principle
The parallel arrangement of liquid crystal molecules along grooves
When coming into contact with grooved surface in a fixed direction, liquid crystal molecules line up parallel along the grooves.

3. Operating Principle
Molecules movement
Offline (no voltage is applied)
Along the upper plate : Point in direction 'a'
Along the lower plate : Point in direction 'b‘
Forcing the liquid crystals into a twisted structural arrangement. (Resultant force)

3. Operating Principle
Light movement
Offline (no voltage is applied)
Light travels through the spacing of the molecular arrangement.
The light also "twists" as it passes through the twisted liquid crystals.
Light bends 90 degrees as it follows the twist of the molecules.
Polarized light pass through the analyzer (lower polarizer).

3. Operating Principle
Molecules movement
Online (voltage is applied)
Liquid crystal molecules straighten out of their helix pattern
Molecules rearrange themselves vertically (Along with the electric field)
No twisting thoughout the movement
Forcing the liquid crystals into a straight structural arrangement. (Electric force)

3. Operating Principle
Light movement
Online (voltage is applied)
Twisted light passes straight through.
Light passes straight through along the arrangement of molecules.
Polarized light cannot pass through the lower analyzer (lower polarizer).
Screen darkens.

3. Operating Principle
Sequences of offline and online mode
Offline
Surrounding light is polarized on the upper plate.
Light moves along with liquid crystals and twisted at right angle.
Molecules and lights are parallel to the lower analyzer.
Light passes through the plate.
Screen appear transparent.

3. Operating Principle
Sequences of offline and online mode
Online
Surrounding light is polarized on the upper plate.
Light moves along with liquid crystals which moves straight along the electric field.
Molecules and lights are perpendicular to the lower analyzer.
Light cannot pass through the plate.
Screen appear dark.

3. Operating Principle
Polarization of light
When unpolarized light passes through a polarizing filter, only one plane of polarization is transmitted. Two polarizing filters used together transmit light differently depending on their relative orientation.

3. Operating Principle
Construction of
Liquid Crystal Display
Two bounding plates (usually glass slides), each with a transparent conductive coating (such as indium tin oxide) that acts as an electrode;
A polymer alignment layer : undergoes a rubbing process as grooves.
Spacers to control the cell gap precisely;
Two crossed polarizers (the polarizer and the analyzer);
Polarizers are usually perpendicular to each other.

3. Operating Principle
Properties of LCD Display
Small footprint (approx 1/6 of CRT)
Light weight (typ. 1/5 of CRT)
power consumption (typ. 1/4 of CRT)
Completely flat screen - no geometrical errors
Crisp pictures - digital and uniform colors
No electromagnetic emission
Fully digital signal processing possible
Large screens (>20 inch) on desktops
High price (presently 3x CRT)
Poor viewing angle (typ. 50 degrees)
Low contrast and luminance (typ. 1:100)
Low luminance (typ. 200 cd/m2)

3. Operating Principle
Advantage of LCD over CRT
Smaller size—AMLCDs occupy approximately 60 percent less space than CRT displays—an important feature when office space is limited.
Lower power consumption—AMLCDs typically consume about half the power and emit much less heat than CRT displays.
Lighter weight—AMLCDs weigh approximately 70 percent less than CRT displays of comparable size.
No electromagnetic fields—AMLCDs do not emit electromagnetic fields and are not susceptible to them. Thus, they are suitable for use in areas where CRTs cannot be used.
Longer life—AMLCDs have a longer useful life than CRTs; however, they may require replacement of the backlight.

4. Display Addressing
Addressing is the process by which pixels are turned on and off in order to create an image.
There are two main types of addressing, direct and multiplexing.
Direct addressing is convenient for displays where there are only a few elements that have to be activated. With direct addressing, each pixel in the display has its own drive circuit. A microprocessor must individually apply a voltage to each element. A common application of direct addressing is the traditional seven segment liquid crystal display, found in wristwatches and similar devices.
4. Display Addressing
In multiplex addressing, a larger number of pixels are involved. When the elements are in a regular order, they can be addressed by their row and column instead of each element being driven separately. This reduces the complexity of the circuitry because each pixel no longer needs its own driver circuit.
If you have a 10x10 matrix of pixels, with direct addressing, you need 100 individual drivers. However, if you use multiplex addressing, you only need 20 drivers, one for each row and one for each column.
This is a tremendous advantage, especially as displays become larger and larger.

4. Display Addressing
Optical Response
twisted nematic displays can switch between light and dark states, or somewhere in between (grayscale).
Electro-distortional curve is shown as follows :

the electro-distortional response determines the transmission of light through the cell.
Different light intensity of an image projected on the screen is determined by different voltage suppy. Thus the level of blocking of light may vary.

5. Applications
A) Thin Film Transistor (TFT)
Constructed on a glass surface using a photolithographic process.
The source and gate are the control electrodes. The drain electrode connects to the liquid crystal pixel. The thin layer of amorphous silicon is the semiconducting material that allows the TFT to function. The capacitor is attached to the pixel electrode, but is not an integral part of the TFT.

5. Applications
B) Alpha-numeric display
Digital letters can be displayed by blocking the lights in different plates we place.
For applications such as digital watches and calculators, a mirror is used under the bottom polarizer. With no voltage applied, ambient light passes through the cell, reflects off the mirror, reverses its path, and re-emerges from the top of the cell, giving it a silvery appearance.
When the electric field is on, the aligned LC molecules do not affect the polarization of the light. The analyzer prevents the incident light from reaching the mirror and no light is reflected, causing the cell to be dark. When the electrodes are shaped in the form of segments of numbers and letters they can be turned on and off to form an alpha-numeric display.

5. Applications
C) Back lighting systems
Alpha-numeric displays are not very bright because the light must pass through multiple polarizers which severely cut down on the intensity of the light, in addition to the various layers of the display which are only semi-transparent.  Therefore a more intense source is employed in the form of a back lighting system.
For brighter displays
Light bulbs mounted behind
At the edges of the display replace the reflected ambient light.
Disadvantage : very power intensive.  Back lighting systems are used in more complex displays such as laptop computer screens, monitors, LCD projectors, pda, digital devices such as digital camera and DV.





08-12-2011, 10:49 AM
Post: #5
RE: lcd display
hello sir,
i need your faver,i am working on lcd module and thair is the problem in lcd module that they will become black at customer end, i have done so many tast but they cn,t black in our end. so what is the promble or what type of test we have done on it. we have used lcd module in speedometer,temprature meter on others.
pls guide me, or send me the info. abot lcd.

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