Learning Examples | Foundations | Hacking | Links
Examples > Libraries > LiquidCrystal
LiquidCrystal
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.
This example sketch prints "Hello World!" to the LCD and shows the time in seconds since the Arduino was reset.
output of the sketch on a 2x16 LCD
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:
A 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.
A Read/Write (R/W) pin that selects reading mode or writing mode
An Enable pin that enables writing to the registers
8 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+ and BKlt-) 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 2x16 LCD in 4-bit mode.
NOTE: The LiquidCrystal library has undergone revisions after Arduino version 0016. Thanks to Limor Fried for the rewrite to include 4-bit and 8-bit modes and more functionality. If you are running Arduino 0016 or earlier, please download the current version of the LiquidCrystal library and install it in your hardware/libraries folder.
Users of 0017 and later will not need to install the update.
Other LiquidCrystal Library Examples
- Hello World - displays "hello world!" and the seconds since reset
- Blink - control of the block-style cursor
- Cursor - control of the underscore-style cursor
- Display - quickly blank the display without losing what's on it.
- Text Direction - control which way text flows from the cursor
- Autoscroll - automatically scroll new text
- Serial input - accepts serial input, displays it
- SetCursor - set the cursor position
- Scroll - scroll text left and right
Circuit
- LCD RS pin connected to digital I/O pin 12
- LCD enable pin connected to digital I/O pin 11
- LCD pins D4 - D7 connected to digital I/O pins 5 through 2, respectively
- LCD voltage and ground connected to +5V and ground
- LCD Vo pin, which controls the contrast, connected to a potentiometer. Adjust the potentiometer to get the text to display at the contrast ratio you want.
Note: This wiring diagram is different than the one for previous versions of the LiquidCrystal library. The R/W pin is connected to ground, and the Enable pin is moved over to pin 11, saving you one I/O pin for other uses.
click the image to enlarge
image developed using Fritzing. For more circuit examples, see the Fritzing project page
Schematic:
click the image to enlarge
