Introduction: How to Connect a Serial LCD to an Arduino UNO

In this instructable I will show you how I connected a serial LCD 16X2 to an Arduino UNO.

There are lots of instructables and tutorials showing you how to connect a regular LCD to an Arduino but not many showing a serial LCD and on my Arduino the PINS to attach the UART pins are hidden. With this instructable I will shed some light on this issue :)

One of the reasons why you would be using a serial LCD is the fact that it uses only 4 PINS instead of 16.

The UART or serial module that is attached to the back of the LCD is responsible for sending and receiving serial communications between the Arduino and the LCD and it has a onboard potentiometer to adjust the brightness of the screen.

What you need for this project is:

  1. An Arduino UNO
  2. Serial LCD a 16X2
  3. and 4 jumper wires male to female.

Step 1: Connect the Electronics

I will use 4 colored jumper wires to make it easy.

There are 4 pins on the UART labeled GND, VCC, SDA and SCL.

Use the red wire to connect the VCC from the UART to the VCC on the Arduino

Use the black wire to connect the GND from the UART to the GND on the Arduino

Use the green Wire to connect the SDA from the UART to the SDA on the Arduino

And finally use the yellow wire to connect the SCL from the UART to the SCL on the Arduino


The SDA and SCL PINS on the Arduino are labeled on the back of the board, use the pictures as guidelines

This is it for wiring, it is easy. Then load the Arduino IDE and upload the sketch to the Arduino.

Step 2: The Sketch

Step one is to download the Liquid Crystal library if you haven't done so already.

I will add a zip file with the library for Windows or you can go the site and download it yourself.

Once you have the library, extract the contents in the Arduino library folder on your computer. On my computer the default location was C:\programfiles\Arduino\library.

I attached a copy of the sketch I used in this instructable,

Here is the breakdown:

First you need to load the libraries, we will load wire.h, LCD.h and LiquidCrystal_I2C.h

//load libraries
#include wire.h

#include LCD.h

#include LiquidCrystal_I2C.h

Then we need to define variables... in this section just copy it as is because it tells the IDE where to find the PCF8574A and how to interact with the LCD to turn on the backlight, the read pin, the write pin and data pins etc...

//Define variables

#define I2C_ADDR 0x27 //Define I2C Address where the PCF8574A is


#define En_pin 2

#define Rw_pin 1

#define Rs_pin 0

#define D4_pin 4

#define D5_pin 5

#define D6_pin 6

#define D7_pin 7

Another line is needed to initialize the LCD, this is done through an array which includes the variables that we defined earlier.

//Initialise the LCD
LiquidCrystal_I2C lcd(I2C_ADDR, En_pin,Rw_pin,Rs_pin,D4_pin,D5_pin,D6_pin,D7_pin);

In the void set up, we start by telling the IDE that we are dealing with a 16X2 LCD

lcd.begin (16,2);

Then I turn on the back light (always good to have a lit LCD), notice it is the same variable from above...


Then I tell it to go to the first line at left most position lcd.setCursor(0,0);

and print lcd.print("I just made an");

then move the cursor to the second line and the left most position lcd.setCursor(0,1);

and print: lcd.print("Instructable :)");

There is void loop because the program need a loop to compile but it should remain empty.

And that's it.... very simple, if you follow these instructions the LCD will output anything you type in this code.

There is a detailed video in the next step.

Step 3: Step by Step Video

Step 4: End Result

If you follow the steps in the instructable The LCD should print out "I made and an Instructable :)"

Happy making