Tutorial: LCD using only 2 arduino pins (with PCF8574 and I2C)

On this tutorial, we will learn how to use a standard 16x2 LCD with Arduino, but using just 2 pins. The magic behind is done by the PCF8574, an I/O expander that communicates with the micro-controller by I2C. If you want to learn about the PCF8574, check this previous tutorial.

Firstly, you have to download the library, there are different downloads for the 1.0 and 0022 Arduino versions:

After that, extract the files to your libraries folder inside your Arduino installation.

Get your breadboard and build the circuit show in the first picture.

Open your Arduino IDE and go to File > Examples > LiquidCrystal_I2C and select "Hello World". The following code will open:

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

LiquidCrystal_I2C lcd(32,16,2); // set the LCD address to 0x20 for a 16 chars and 2 line display

void setup()
{
    lcd.init(); // initialize the lcd 

    // Print a message to the LCD.
    lcd.backlight();
    lcd.print("Hello, world!");
}

void loop()
{
}

Upload your code. You may need to turn the potentiometer to adjust the LCD contrast. You now show see the words "Hello, world!" on your display.

References:

http://arduino.cc/playground/Code/LCDi2c

http://hmario.home.xs4all.nl/arduino/LiquidCrystal_I2C/

Views: 45008

Tags: arduino, i2c, lcd, pcf8574, tutorial

Comment by Mario_H on September 3, 2012 at 4:27pm

 

Just found the link to my library here and I would advise to add three resistors to the schematic above.

Two 4K7 pull-up resistors on the I2C lines (see I2C specifications).

And one current limiting resistor in series with the backlight LED to prevent damage to the backlight LED.

To calculate the correct limiting resistor you need the datasheet of the LCD.

Comment by Rob Whight on October 16, 2012 at 3:33am

Haven't got myself an LCD display yet (on day 2 with my Arduino !). Very interested in this circuit. Note it only uses two pins - would that mean that I could drive more than one display at the same time and if so, how do I go about send data to different displays ? Thx

Comment by Mario_H on October 16, 2012 at 4:32am

Yep, you can connect multiple displays to the I2C port.

Give each PCF8574 another address (using pins 1,2 and 3).

 

In the sketch define two lcd's

LiquidCrystal_I2C lcd1(0x20,16,2); // set the first LCD address to 0x20

LiquidCrystal_I2C lcd2(0x21,16,2); // set the second LCD address to 0x21

 

Initialize them in the setup-section:

lcd1.init(); // initialize the 1st lcd

lcd2.init(); // initialize the 2nd lcd

 

And send text:

lcd1.print("1st Hello!");

lcd2.print("2nd Hello!");

That's all.

More examples in the zip you can download from the link above.

Comment by Rob Whight on October 16, 2012 at 10:36am

OK - That's really helpful. The bit I think I'm struggling with is how each display knows which one it is and where it is connected. Is there a relationship between the 0x20 and 0x21 and the pinouts for example ? Appreciate your help for this here newbie !

Comment by Mario_H on October 16, 2012 at 3:32pm

On the hardware side you give each PFC an unique address (with pins 1-3).

To use them in the sketch:

First you define lcd1 as the one on address 0x20

Next you define lcd2 as the one on address 0x21

During the rest of the sketch you refer to lcd1 when you want to write to the first lcd and to lcd2 when you want to write to the second one.

So the LCD itself isn't aware of which one it is, it just displays the data it receives.

The selection is done by addressing the PCF. All data not sent to the configured address of a PCF is simply ignored. And just for clarity: to control two displays via I2c you need two of the circuits shown above.

Comment

You need to be a member of GarageLab (arduino, electronics, robotics, hacking) to add comments!

Join GarageLab (arduino, electronics, robotics, hacking)

Latest Activity

GarageLab posted blog posts
11 hours ago
Raghuvir G posted discussions
17 hours ago
Jagajeet K posted a discussion

Digital IO – LED Blink – Arduino for Beginners

I have a doubt in the below link  …in that I used 220 ohm resistor for LED …Is Resistor have any…See More
18 hours ago
Profile IconRalph Wade, Jagajeet K, Raghuvir G and 1 more joined GarageLab (arduino, electronics, robotics, hacking)
yesterday
GarageLab posted blog posts
Tuesday
Enrico M. posted a status
"Building the Apollo console version I"
Monday
Lena Cook is now a member of GarageLab (arduino, electronics, robotics, hacking)
Monday
Paul Denton updated their profile
Nov 21
GarageLab posted a blog post
Nov 21
Profile IconRichard Coplan and Juan V. Sanchez-Andres joined GarageLab (arduino, electronics, robotics, hacking)
Nov 21
Kshitij Dadhekar commented on GarageLab's blog post Tutorial: How to use the Cellular Shield (SM5100B) with Arduino
"Hello,       Can you tell me what is the resistance of the speaker to be…"
Nov 19
GarageLab posted a blog post
Nov 19
Profile IconKshitij Dadhekar, Marvellous Mark and Enrico M. joined GarageLab (arduino, electronics, robotics, hacking)
Nov 19
david chan commented on GarageLab's blog post Tutorial: Humidity and Temperature Sensor with Arduino
"How do you see the output "
Nov 18
Enrico M. posted a discussion

Power supply circuit

Hi guys,I'm building some sort of wood case to arduino mega with LCD, keypad, LED's ...I also want…See More
Nov 18
GarageLab posted blog posts
Nov 18
Profile Icondavid chan, uday harihar, CVassiliou and 4 more joined GarageLab (arduino, electronics, robotics, hacking)
Nov 18
Jeff Bowen updated their profile
Nov 17
Michael Shaw replied to Jean-Guillaume LALANNE's discussion Smallest Arduino with BLE stack and push button integrated
"Check out Tiny circuits for open source: https://tiny-circuits.com/"
Nov 16
rozzers commented on rozzers's video
Nov 14

© 2014   Created by Marcelo Rodrigues.

Badges  |  Report an Issue  |  Terms of Service