LCD and Keypad

Introduction

In the previous tutorial, we have discussed 7-segment. Now, we are going to learn how to work with LCD and Keypad.

LCD

LCD is used to write parameters and status. We have a 16x2 LCD (16 columns and 2 rows). It has 16-pins.

Connect an LCD to an Arduino in SimulIDE

Let’s put an LCD on the board. To do that we can use Outputs/Displays/HD44780. After putting that on the board, we should connect the pins of it like below:

• RS: 12
• RW: ground
• E: 11
• D4: 5
• D6: 4
• D7: 3
• D8: 2

The result should be something like below:

Liquid Crystal

Liquid Crystal is a well-known package that helps us to work with LCD. This package contain so many great and useful functions. You can see the list of all functions in this link.

Add LiquidCrystal to PlatformIO

To add LiquidCrystal to a PlatformIO project we should add this code to platformio.ini.

lib_deps =
  arduino-libraries/LiquidCrystal

This code will download the LiquidCrystal and then you can import it in your main.cpp like below:

#include <LiquidCrystal.h>

Make an LCD Object

Now, let’s make an LCD object using LiquidCrystal. To do so, we can use the code below:

const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7 = 2;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

In the code above, at first we defined the pins in a way that we connected them to our Arduino Uno. Then, we made an object of LiquidCrystal with those pins with the name of lcd. We put that code on top of the setup and loop function to be global. Now, let’s talk about the functions that we can use for this object.

begin

This function initializes the LCD. It automatically sets all the pin modes and should be called before any other LCD commands.

The usual syntax that we use:

lcd.begin(cols, rows);

Example:

lcd.begin(16, 2);

write

Write a character on the LCD.

Syntax:

lcd.write(ch);

Example:

lcd.write('h');

print

Write a text on the LCD.

Syntax:

lcd.print(text);

Example:

lcd.print("Hello World!");

setCursor

Jumps to the given column and row.

Syntax:

lcd.setCursor(col, row);

Example:

lcd.setCursor(5, 1);

clear

Clears the LCD and jumps to the start.

lcd.clear();

Example:

lcd.clear();

LCD Hello World

Now, that we know about Liquid Crystal and the functions that we can use, let’s write a simple example. We want our LCD to show hello at the first row, starting from the 3rd column. After some pause, clear the hello and show world at the second row starting from the 4th column. Your output should be something like below:

Keypad

Keypad is a series of keys in a matrix. It contains of keys in rows and columns. For example, if we have 4 rows and 3 columns we would have 12 keys. The advantage that a keypad gives us is that we don’t require to occupy 12 pins to control 12 keys. Instead, we only need 7 pins, 4 for rows and 3 for columns. Here is an example of a Keypad in SimulIDE.

Add Keypad to Arduino Uno in SimulIDE

Now, let’s add a keypad to our Arduino Uno in our SimulIDE. We can access to the Keypad in Switches/Keypad. When you put it on the board, you can see there are 4 rows and 3 columns. Let’s connect each row and column like below:

• row-0: 0
• row-1: 1
• row-2: 6
• row-3: 7
• col-0: 8
• col-1: 9
• col-2: 10

You should have something like this:

Add Keypad to PlatformIO

To use Keypad in Arduino, we can use a library called Keypad. We can simply add Keypad to our PlatformIO project by adding it to the lib_deps in platformio.ini, like below:

lib_deps =
  ...
  Keypad

Now we are able to import it like in our main.cpp like below:

#include <Keypad.h>

Make a keypad Object

To create a object for our Keypad we should at first define a matrix for our keys like below:

const byte ROWS = 4;
const byte COLS = 3;

char keys[ROWS][COLS] = {
    {'1', '2', '3'},
    {'4', '5', '6'},
    {'7', '8', '9'},
    {'*', '0', '#'}};

As you can see, we have defined two constants called ROWS and COLS which each of them represent how many rows and columns we have. Then we defined our matrix of keys in a way that we have them in our Keypad. Now, it’s time to define which pins are connected to each row and column. To do that we can write something like below:

byte rowPins[ROWS] = {0, 1, 6, 7};
byte colPins[COLS] = {8, 9, 10};

As you recall, in our simulation we have connected our rows to the pins of 0, 1, 6, 7 and columns to 8, 9, 10. We defined rowPins and colPins to have those values. Now, let’s define our Keypad Object. To do so, we can use the code below:

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

As you can see, in the code above, we have used Keypad class to create an instance of a Keypad. For the first argument, we changed our keys which were in a matrix to the format that Keypad likes, using makeKeymap function. Then for the other arguments, we gave rowPins, colPins, ROWS, and Cols respectively. We named our object keypad which we are going to use it later. Now, let’s talk about the function that we are mostly going to use.

getKey

A function that checks if any keys is pressed. If a key was pressed, it would return the respective key and if not it would return 0.

Syntax:

keypad.getKey();

Example:

char key = keypad.getKey();

Keypad to LCD

Now, let’s write a program that displays the output of the KeyPad on the LCD. Your output should be like this:

Login system

Now, let’s write a login system. We have a username and password stored in our code (hard codded). We want user to enter a username and password. After that we are going to check if he has entered the correct ones or not. If it was correct we tell him it is correct, otherwise we tell him it was incorrect. Your output should be something like below:

• Correct username: 12
• Correct password: 5662
• Enter: #

Conclusion

In this tutorial, we learned how to use LCD and Keypad in Arduino Uno. First, we explained what LCD is and how to use LiquidCrystal to control it. Then we explained the most important functions and provided an example. After that, we talked about Keypad. We introduced a library with the same name to control it. Then, we combined LCD and Keypad. Finally, we provided an example to make you understand these concepts better.