Components » HD44780 Text LCD

HD44780 Text LCD

Controlling text LCD panels, which use the HD44780 LCD display driver.

Hello World

Import program TextLCD_HelloWorld

Simple Hello World! for the TextLCD library

Library

Import library TextLCD

TextLCD library for controlling various LCD panels based on the HD44780 4-bit interface

Notes

Pin number	TextLCD pins	mbed pins
1	GND	0V
2	VCC	3.3V
3	VO	0V, via 1k resistor
4	RS	p15
5	RW	0V
6	E	p16
7	D0	not connected
8	D1	not connected
9	D2	not connected
10	D3	not connected
11	D4	p17
12	D5	p18
13	D6	p19
14	D7	p20

Warning

The contrast VO pin seems to have different behaviour on different displays, so you may need to experiment for your display to see anything. I think I've seen some work tied to 0V, some to 3.3V, or with a different resistor.

Adjustable contrast can be achieved with a 10k trim-pot in a voltage divider configuration: one side to Vcc, other side to GND, wiper to VO. Adjust until you see a line of solid squares, then back off until they just disappear.

Some displays need a negative voltage at VO. One side of the trimpot is connected to the negative voltage instead of GND in that case. F.i. a Maxim MAX1044 can be used to generate the negative voltage.

Different LCD Panel Sizes

Setting the type field in the TextLCD constructor allows configuration for the different display panel sizes:

TextLCD::LCD16x2     16x2 LCD panel (default) 
TextLCD::LCD16x2B    16x2 LCD panel alternate addressing 
TextLCD::LCD20x2     20x2 LCD panel 
TextLCD::LCD20x4     20x4 LCD panel

Note: There is now also support for

TextLCD::LCD8x1    8x1 LCD panel
TextLCD::LCD8x2    8x2 LCD panel
TextLCD::LCD16x1  16x1 LCD panel
TextLCD::LCD16x4  16x4 LCD panel
TextLCD::LCD24x2  24x2 LCD panel
TextLCD::LCD24x4  24x4 LCD panel (for KS0078 controller)
TextLCD::LCD40x2  40x2 LCD panel
TextLCD::LCD40x4  40x4 LCD panel (two controllers)

You can find the new lib here

For example:

#include "mbed.h"
#include "TextLCD.h"

TextLCD lcd(p15, p16, p17, p18, p19, p20, TextLCD::LCD20x4); // rs, e, d4-d7

int main() {
    lcd.printf("Hello World!\n");
}

Enhanced Version of Text LCD

An enhanced forked version of the original Text LCD is here

Reference

The underlying HD44780 chip is a driver used in many LCD character displays. It might sometimes be referred to as Hitachi HD44780U. There are also several compatible clones of this chip in use (eg Samsung KS0066).