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Introduction

LCD library

Welcome to the LCD Library for Arduino and Chipkit. It is a derivate of the original LiquidCrystal Library as sourced in the Arduino SDK. It has been developed to be compatible with the current LiquidCrystal library, its performance is almost 5 times faster and fully extendable if need be.

Being faster, gives your applications more time to do more things than just controlling the LCD. So, its cool, you can do more stuff.

It supports most Hitachi HD44780 based LCDs, or compatible, connected to any project using: 4, 8 wire parallel interface, I2C IO port expander and Shift Regiter.

It currently supports 4 types of connections:

Contributors

The library has had the invaluable contribution of:

  • piccaso - Florian Fida - Flo, thanks for testing and improving the SR library, initial version of the 1 wire interface and speed improvements.
  • B. Perry - bperrybap@opensource.billsworld.billandterrie.com, with his thoughtful contribution, speed improvements and development support for the SR2W library.

There is a nice freebe in the library: fastIO. This is a collection of fast digital read write operations originally writen by Florian Fida that makes the ShiftRegister modes of operations as fast as the 4bit parallel LCD.

Library Overview

This library provides the same interface to applications as the LiquidCrystal library sourced by the Arduino SDK. The main changes to the LiquidCrystal Library is that it has been changed to be a pure abstract class from which particular implementations derive from.

All the basic functions to control an LCD are implemented in the base class, while the particular way to "talk" to the LCD is done by a class that simply knows how to write to the LCD.

Therefore, it is possible to create new drivers to the library by simply inhering from the base class and develop the functions that are specific to "talk" to the LCD.

The library currently supports 3 types of connections:

  • 4 bit parallel LCD interface
  • 8 bit parallel LCD interface
  • I2C IO bus expansion board with the PCF8574* I2C IO expander ASIC.
  • ShiftRegister adaptor board (please visit the HW schematics and configuration for details).

The LCD library started as a base support for the PCF8574* I2C IO expander ASIC in the LCDI2CextraIO board but it has rapidly grown to support other LCD driving mechanism due to the simplicity of adding new drivers to it.

Since this library is a full class hierarchy, new interfacing mechanisms can be added without having to re-write the entire driver. Drivers for the MCP2300, SPI and Serial are very easy to develop since you would only have to worry about how to write to the particular new device.

Usage

The library is used just like the current stock LiquidCrystal LCD library. You only have to tell it what type of LCD and how you have connected to your project and you are set. The main difference is that the LCD library is a "collection" of libraries with the same common interface (a class hierarchy with a base abstract class - in the technical jargon).

Here is how to use the library for a 4 bit LCD interface:

#include <LiquidCrystal.h>

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
#define   CONTRAST_PIN   9
#define   BACKLIGHT_PIN  7
#define   CONTRAST       125

void setup()
{
  // Switch on the backlight and LCD contrast levels
  pinMode(CONTRAST_PIN, OUTPUT);
  pinMode(BACKLIGHT_PIN, OUTPUT);

  digitalWrite(BACKLIGHT_PIN, HIGH);
  analogWrite (CONTRAST_PIN, CONTRAST);
    
  lcd.begin(16,2);               // initialize the lcd 

  lcd.home ();                   // go home
  lcd.print("Hello, ARDUINO ");  
  lcd.setCursor ( 0, 1 );        // go to the next line
  lcd.print (" WORLD!");      
}

void loop()
{

}

Here's of how to use the library for a I2C LCD interface using the I2CLCDextraIO board or similar:

#include <Wire.h> 
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x38);  // Set the LCD I2C address

#define BACKLIGHT_PIN     13

void setup()
{
  // Switch on the backlight
  pinMode ( BACKLIGHT_PIN, OUTPUT );
  digitalWrite ( BACKLIGHT_PIN, HIGH );
  
  lcd.begin(16,2);               // initialize the lcd 

  lcd.home ();                   // go home
  lcd.print("Hello, ARDUINO ");  
  lcd.setCursor ( 0, 1 );        // go to the next line
  lcd.print (" WORLD!  ");      
}

void loop()
{

}

Being a "collection" of libraries with a common interface, you can develop a complete project just by using a reference to the base LCD class (a pointer to an "LCD variable") and then in the project (sketch) and during the initialization (setup routine) you would just have to pass the "concrete" LCD that you are using.

This is particularly useful for projects that have a MMI built-in where you would like to use it with multiple LCDs maintaining the user interface hidden from the particular LCD you are using. It is also very useful if you have a project and you don't know how you are going to connect the LCD or your change your mind halfway through the project.

Using the virtual LCD class in projects:

#include <Wire.h>
#include <LCD.h>
#include <LiquidCrystal_I2C.h>

#define BACKLIGHT_PIN     13

LiquidCrystal_I2C lcd(0x38);  // Set the LCD I2C address
LCD *myLCD = &lcd;

void setup()
{
  // Switch on the backlight
  pinMode ( BACKLIGHT_PIN, OUTPUT );
  digitalWrite ( BACKLIGHT_PIN, HIGH );
  
  myLcd->begin(16,2);               // initialize the lcd 

  myLcd->home ();                   // go home
  myLcd->print("Hello, ARDUINO ");  
  myLcd->setCursor ( 0, 1 );        // go to the next line
  myLcd->print (" WORLD!  ");      
}

void loop()
{

}

The only difference is the "include" and how you initialize the LCD. Not a bit difference, right!

When you install the library it may come out with a compilation error. This is due to the fact that it can't find the Wire library header files. Please include Wire.h at the beginning of your sketch. Why? Because of the peculiarities of the Arduino compilation environment. I am working on a way to work around this.

The library is configured by default to run fast. Should you have problems with slow LCDs, you will have to disable the FAST_MODE in the LCD.h header file of the library by simply commenting the FAST_MODE define.

Tests

All the HW configurations described in the HW section have been tested, the last one was the ShiftRegister adaptor by piccaso and the 1 wire interface by Stephen Erisman, thanks for sharing and testing.

The code has been fully tested with a 4 bit interface and with the I2CLCDextraIO (companion board to this library) using the PCF8574* ASIC.

Performance and Benchmakrs

Each supported and tested library class has gone through a performance benchmark and it is compared with respect to the original LiquidCrystal library.

AVR bench marks:

  • AVR @ 16MHz
  • I2C @ 100KHz

ChipKit Uno32:

  • PIC32 @ 80MHz

ShiftRegister class benched marked by piccaso - flo, thanks for testing it and sharing.

Benchmark 1: write every position of the LCD one by one, 10 cycles.

Benchmark 2: write a bar graph using the entire LCD to draw the bars. This has 5 writes per LCD position, 10 cycles.

Benchmark 3: write a string to each row of the LCD from a string in RAM, 10 cycles.

Benchmark 4: write a string to each row of the LCD from a string stored in FLASH, 10 cycles.

Benchmark Results

The execution time is based on the sample benchmark file using FAST_MODE enabled.

Execution time

                LiquidCrystal    4BIT        ShiftRegister    ShiftRegister SR3W        I2C         
benchmark1      11055 us         2966 us     2576 us          3519 us                   32062 us    
benchmark2      125770 us        34660 us    29224 us         39839 us                  362954 us   
benchmark3      13660 us         3616 us     3198 us          4370 us                   39613 us    
benchmark4      13643 us         3597 us     3180 us          4352 us                   39610 us    

Average LCD write operation time

                LiquidCrystal      4BIT        ShiftRegister     ShiftRegister SR3W     I2C         1WSR
write op.       325 us             87 us       75.92 us             103.72 us           943.61 us   ... us

Performance ratio vs LiquidCrystal library

                LiquidCrystal      4BIT        ShiftRegister     ShiftRegister SR3W     I2C         1WSR
Performance     1                  3.72        4.28              3.13                   0.34        3.8

Benchmark II

16MHz AVR

Interface    ByteXfer    16x2FPS      Ftime
----------------------------------------------
4BIT          338uS        86.92     11.51ms (orignal Arduino IDE Liquid Crystal)
4BIT           98uS       298.58      3.35ms
SR2W           76uS       388.62      2.57ms
SR_2W          72uS       406.90      2.46ms
SR_3W          61uS       480.03      2.08ms
SR3W          102uS       287.92      3.47ms
I2C           957uS        30.74     32,25ms
SR1W_HC        94uS       311.41      3.21ms
SR1W_SC       116uS       252.83      3.96ms 

80Mhz Pic32 (ChipKit Uno32)

4BIT          232uS       126.73      7.89ms (orignal mpide Liquid Crystal)
4BIT           57uS       517.41      1.93ms
SR2W           53uS       557.35      1.79ms
SR_2W          53uS       554.66      1.80ms
SR_3W          50uS       591.40      1.69ms
SR3W           56uS       524.91      1.91ms

HW configuration, schematics and initialization of different boards and configuration

Please visit the HW configuration schematics of all the tested configurations of the library.

HW schematics

Downloading and Installation

Source code for the library and documentation can be downloaded from the download section of this repository: here

The library comes in source and with examples that will get you started. Additionally you have a full description of the library in the docs folder in HTML format that you can browse.

To install the library:

  • Download the most recent version of the library.
  • Extract the library. It should be in a subfolder of its own (something like /myLCDSketch/libraries/LCD) in your sketch or in the library folder of the Arduino distribution.
  • When you start the Arduino IDE, it should contain a new menu "LCD" with examples. (File > Examples > LCD...). It should also appear in the menu Sketch > import library.
  • Alternatively you can install the library in the Arduino SDK library pool. To install and learn about libraries please follow the instructions in Library Tutorial, there is a Section in the Tutorial indicating how to install a library.

The library has been developed to replace the current Arduino library, therefore you will need to remove/backup the LiquidCrystal folder from the Arduino library folder the original LiquidCrystal library and replace it for this one. You will also potentially need to remove other LCD libraries like LiquidCrystal_I2C as that will also conflict with this library.

Also in the download section you can find the I2CIO driver library for the PCF8574* I2C IO expander ASIC.

Version

Current New LiquidCrystal is the latest zip file in the download section.

The New LiquidCrystal library has been tested and is compatible with Arduino SDK 1.0.1, 1.0 and Arduino SDK 0022.

This library has also been tested with the chipKit.

Minor changes would have to be done to be compatible with previous versions of the SDK.

Licensing

Lets keep this section very short.

New LiquidCrystal Library by F. Malpartida is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License. CC BY-SA 3.0

This work was inspired on the Arduino SKD "LiquidCrystal" library and the "LiquidCrystal_I2C" library from Mario_H.

Have fun!

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