Liquid-crystal display

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liquid-crystal display (LCD) is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals. LCDs are used in a wide range of applications including computer monitors, televisions, instrument panels, aircraft cockpit displays, and signage. They are common in consumer devices such as video players, gaming devices, clocks, watches, calculators, and telephones, and have replacedcathode ray tube (CRT) displays in most applications. They are available in a wider range of screen sizes than CRT and plasma displays, and since they do not use phosphors, they do not suffer image burn-in. LCDs are, however, susceptible to image persistence.

The LCD screen is more energy efficient and can be disposed of more safely than a CRT. Its low electrical power consumption enables it to be used in battery-powered electronic equipment. It is an electronically modulated optical device made up of any number of segments filled with liquid crystals and arrayed in front of a light source (backlight) or reflector to produce images in color or monochrome.

LiquidCrystal library – 

The LiquidCrystal library allows you to control LCD displays that are compatible with the Hitachi HD44780 driver. There are many of them out there, and you can usually tell them by the 16-pin interface.

The LCDs have a parallel interface, meaning that the microcontroller has to manipulate several interface pins at once to control the display. The interface consists of the following pins:

register select (RS) pin that controls where in the LCD’s memory you’re writing data to. You can select either the data register, which holds what goes on the screen, or an instruction register, which is where the LCD’s controller looks for instructions on what to do next.

Read/Write (R/W) pin that selects reading mode or writing mode

An Enable pin that enables writing to the registers

data pins (D0 -D7). The states of these pins (high or low) are the bits that you’re writing to a register when you write, or the values you’re reading when you read.

There’s also a display constrast pin (Vo)power supply pins (+5V and Gnd) and LED Backlight (Bklt+ andBKlt-) pins that you can use to power the LCD, control the display contrast, and turn on and off the LED backlight, respectively.

The process of controlling the display involves putting the data that form the image of what you want to display into the data registers, then putting instructions in the instruction register. The LiquidCrystal Library simplifies this for you so you don’t need to know the low-level instructions.

The Hitachi-compatible LCDs can be controlled in two modes: 4-bit or 8-bit. The 4-bit mode requires seven I/O pins from the Arduino, while the 8-bit mode requires 11 pins. For displaying text on the screen, you can do most everything in 4-bit mode, so example shows how to control a 2×16 LCD in 4-bit mode.

Member Functions :

begin() – 

Specifies the dimensions (width and height) of the display.

Syntax

lcd.begin(cols, rows)

Parameters

lcd: a variable of type LiquidCrystal

cols: the number of columns that the display has

rows: the number of rows that the display has

clear() – 

Clears the LCD screen and positions the cursor in the upper-left corner.

Syntax

lcd.clear()

Parameters

lcd: a variable of type LiquidCrystal

blink() – 

Display the blinking LCD cursor. If used in combination with the cursor() function, the result will depend on the particular display.

Syntax

lcd.blink()

Parameters

lcd: a variable of type LiquidCrystal

Example

  • blink() and noBlink()

cursor() – 

Display the LCD cursor: an underscore (line) at the position to which the next character will be written.

Syntax

lcd.cursor()

Parameters

lcd: a variable of type LiquidCrystal

Example

  • cursor() and noCursor()

autoscroll() – 

Turns on automatic scrolling of the LCD. This causes each character output to the display to push previous characters over by one space. If the current text direction is left-to-right (the default), the display scrolls to the left; if the current direction is right-to-left, the display scrolls to the right. This has the effect of outputting each new character to the same location on the LCD.

Syntax

lcd.autoscroll()

Parameters

lcd: a variable of type LiquidCrystal

setCursor() – 

Position the LCD cursor; that is, set the location at which subsequent text written to the LCD will be displayed.

Syntax

lcd.setCursor(col, row)

Parameters

lcd: a variable of type LiquidCrystal

col: the column at which to position the cursor (with 0 being the first column)

row: the row at which to position the cursor (with 0 being the first row)

print() – 

Prints text to the LCD.

Syntax

lcd.print(data) 
lcd.print(data, BASE)

Parameters

lcd: a variable of type LiquidCrystal

data: the data to print (char, byte, int, long, or string)

BASE (optional): the base in which to print numbers: BIN for binary (base 2), DEC for decimal (base 10), OCT for octal (base 8), HEX for hexadecimal (base 16).

Returns

byte
print() will return the number of bytes written, though reading that number is optional

EXAMPLE :

Circuit

  • LCD RS pin to digital pin 12
  • LCD Enable pin to digital pin 11
  • LCD D4 pin to digital pin 5
  • LCD D5 pin to digital pin 4
  • LCD D6 pin to digital pin 3
  • LCD D7 pin to digital pin 2

Additionally, wire a 10K pot to +5V and GND, with it’s wiper (output) to LCD screens VO pin (pin3).

LCD_bb

 

Schematic 

LCD_schem

Code

/*
  LiquidCrystal Library - Hello World
 Demonstrates the use a 16x2 LCD display.  The LiquidCrystal
 library works with all LCD displays that are compatible with the 
 Hitachi HD44780 driver. There are many of them out there, and you
 can usually tell them by the 16-pin interface.
 This sketch prints "Hello World!" to the LCD
 and shows the time.
  The circuit:

 * LCD RS pin to digital pin 12
 * LCD Enable pin to digital pin 11
 * LCD D4 pin to digital pin 5
 * LCD D5 pin to digital pin 4
 * LCD D6 pin to digital pin 3
 * LCD D7 pin to digital pin 2
 * LCD R/W pin to ground
 * 10K resistor:
 * ends to +5V and ground
 * wiper to LCD VO pin (pin 3)
*/
// include the library code:
#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

void setup() {
  // set up the LCD's number of columns and rows: 
  lcd.begin(16, 2);
  // Print a message to the LCD.
  lcd.print("hello, world!");
}

void loop() {
  // set the cursor to column 0, line 1
  // (note: line 1 is the second row, since counting begins with 0):
  lcd.setCursor(0, 1);
  // print the number of seconds since reset:
  lcd.print(millis()/1000);
}

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