3 PIN HD44780 LCD

One of the problems of connecting an HD44780 LCD

to an arduino is the number of pins taken up (usually 6). There is an older article here for hooking up an HD44780 LCD to an arduino with only 3 pins.  (Note: There is an alternate link here as the original link may be down.)

The circuit uses the 74HC595 shift register IC.  I liked the idea and have built several of these circuits.

Thus I have a handy way of attaching an LCD to arduino projects without taking too many pins.

You will need a library for controlling the LCD (attached via the 74HC595 shift register) which you can get here. (Updated:  here)  A sample sketch is shown below. It is the same one here from the original author but I modified it via:

lcd.setLED2Pin(HIGH);

to turn the backlight on. Here is the sketch:

/*
 * 3-pin Arduino interface for HD44780 LCDs via 74HC595 Shift Register
 *     by Rowan Simms   code@rowansimms.com
 *     License: Creative Commons - Attribution.
 *     Full Documentation and Description:  http://rowansimms.com/article.php/lcd-hookup-in-seconds
 *
 * This sketch allows Arduinos to use a shift register to control an LCD, allowing
 * a reduction in pins it requires from 6 to 3 while still retaining full control
 * including backlight on/off.
 * This requires the use of the LiquidCrystal595 library
 * available at: http://code.google.com/p/arduino-lcd-3pin/
 */

#include <LiquidCrystal595.h>    // include the library
LiquidCrystal595 lcd(7,8,9);     // datapin, latchpin, clockpin

void setup() {
    lcd.init(7,8,9);
    lcd.setLED2Pin(HIGH);        // Backlight On
    lcd.begin(16,2);             // 16 characters, 2 rows
    lcd.clear();
    lcd.setCursor(0,0);
    lcd.print("Wow. 3 pins!");
    lcd.setCursor(0,1);
    lcd.print("Fabulous!"); 
}

void loop() {
    // not used.
}