Lab 11

Liquid Crystal Display

Liquid crystals are a state of matter intermediate between that of a crystalline solid and an isotropic liquid.

A liquid crystal display device is a passive device. It doesn't produce any light to display characters, images, video; instead it alters the light traveling through it.  Its internal structure is locally altered (pixel by pixel of the display matrix) by the presence of an external electric field, which causes an alteration of the incident light’s polarization state of selective pixels. The concept of controlling the amount of transmitted light by reorienting liquid crystals upon applying electrical field is the basis of the LCD industry today.

Herein, we first pursue to get familiar with the working principle of liquid crystal displays (Sections I and II.) Subsequently, in the experimental section, an Arduino microcontroller is used to operate a commercial LCD display. We will address  controlling the LCD through parallel communication and serial communication methods; the latter uses an I2C adapter that allows driving the LCD with only two input wires. Applications include driving the LCD with 8 bit data bus, as well in a 4-bit data bus modality.   

CONTENTS

I.   Liquid Crystal Displays

  I.1    The discovery

  I.2    Materials involved

  I.3    Principle of operation

  I.4   Internal construction of a LCD-pixel

  I.5   Addressing (driving) the pins of a display:

           Static (direct) vs dynamic (multiplex) methods

  1.6   LCD matrix screens

           1.6.1  Simple Matrix Drive

           1.6.2  Active Matrix Drive

II. Liquid Crystal fundamentals

  II.1  Nematic and cholesteric liquid crystal mesophases

  II.2   Liquid crystal as a birefringent material: Optical properties

           II.2.1   Effect of sample thickness: Controlling light polarization

           II.2.2  Propagation of light in cholesterol liquid crystals

III. Experimental procedure

  III.1  Components of the Liquid Crystal display

          III.1.1  ADM1602K-NSA-FBS-3.3v Liquid Crystal Display

          III.1.2  The serial computer bus  Inter-Integrated Circuit or I2C

          III.1.3  LCD Pin connection

          III.1.4  Instructions Table for the HD44780  LCD module

          III.1.5  Character Table for the HD44780  LCD module

            III.1.6   Arduino LiquidCrystal Library

  III.2  Controlling the Liquid Crystal display through parallel communication

            III.2.1   Getting familiar with the functioning of the LCD device                  

              III.2.1.A   Displaying “Hello World”

              III. 2.1.B  Scrolling the cursor

          III. 2.1.C        Implementing a custom character

      III.2.2  Drive the LCD with 8 bit data bus

      III.2.3  Drive the LCD with 4 bit data bus 

  III.3  Controlling the Liquid Crystal display through serial communication with the I2C Adapter

 III.3.1 Serial-connection  vs  parallel-connection

     III.3.2  Pins

     III.3.3  The role of the I2C  SDA and SCL wires

     III.3.4  Determining the I2C Address

     III.3.5   Implementing a custom character and displaying your name

     III.3.6   Displaying “Portland State University, Physics Dept, PH315”