Why Custom characters on LCD in Arduino? - Purpose & Use Cases

The Big Idea

What if you could turn your boring LCD letters into fun little pictures with just a few lines of code?

The Scenario

Imagine you want to show a special symbol, like a smiley face or a unique icon, on a small LCD screen connected to your Arduino. Without custom characters, you are stuck with only the basic letters and numbers the screen offers.

The Problem

Trying to draw these symbols manually pixel by pixel on the LCD is slow and complicated. You might have to turn on and off individual dots, which is error-prone and takes a lot of code. It's hard to reuse or change these symbols easily.

The Solution

Custom characters let you design your own small pictures by defining which pixels light up. You create a simple pattern once, store it in the LCD's memory, and then display it anytime like a normal letter. This makes your screen more expressive and your code cleaner.

Before vs After

✗ Before

lcd.setCursor(0,0);
lcd.write(0x01); // trying to show a smiley by guessing code

✓ After

byte smiley[8] = {0,10,0,0,17,14,0,0};
lcd.createChar(0, smiley);
lcd.setCursor(0,0);
lcd.write(byte(0));

What It Enables

You can easily add fun icons, symbols, or even simple graphics to your LCD, making your projects more interactive and user-friendly.

Real Life Example

In a weather station project, you can show custom icons like sun, rain, or clouds on the LCD to represent the current weather instead of just text.

Key Takeaways

Manual pixel control on LCD is slow and tricky.

Custom characters let you design and reuse small images easily.

This makes your Arduino displays more expressive and neat.

Practice

1. What is the main purpose of using createChar() in Arduino LCD programming?

easy

A. To clear the LCD screen

B. To define a custom character pattern for the LCD

C. To set the cursor position on the LCD

D. To print a string on the LCD

Solution

1. Step 1: Understand the function of createChar()

   This function is used to define a new character pattern by specifying pixel rows for the LCD.

2. Step 2: Compare with other LCD functions

   Functions like clearing the screen, setting cursor, or printing strings are different and not related to defining custom characters.

3. Final Answer:

   To define a custom character pattern for the LCD -> Option B

4. Quick Check:

   createChar() defines custom characters [OK]

Hint: Remember: createChar defines, write displays [OK]

Common Mistakes:

• Confusing createChar with print or clear functions
• Thinking createChar moves the cursor
• Assuming createChar prints text directly

2. Which of the following is the correct way to declare a custom character array for createChar()?

easy

A. byte smiley[8] = {0, 10, 0, 0, 17, 14, 0, 0};

B. int smiley[8] = {0, 10, 0, 0, 17, 14, 0, 0};

C. char smiley[5] = {0, 10, 0, 0, 17};

D. byte smiley[7] = {0, 10, 0, 0, 17, 14, 0};

Solution

1. Step 1: Check data type and array size

   Custom characters require 8 bytes (one for each row) and use the byte type for pixel data.

2. Step 2: Validate array length and type

   byte smiley[8] = {0, 10, 0, 0, 17, 14, 0, 0}; uses byte type and 8 elements, matching the LCD custom character format.

3. Final Answer:

   byte smiley[8] = {0, 10, 0, 0, 17, 14, 0, 0}; -> Option A

4. Quick Check:

   8 bytes array with byte type = correct declaration [OK]

Hint: Custom chars need 8 bytes, not int or fewer elements [OK]

Common Mistakes:

• Using int instead of byte
• Using fewer than 8 elements
• Using char type which is signed and may cause issues

3. What will be the output on the LCD after running this code snippet?

byte heart[8] = {0,10,31,31,31,14,4,0};
lcd.createChar(0, heart);
lcd.setCursor(0,0);
lcd.write(byte(0));

medium

A. The LCD prints the number 0

B. The LCD shows a blank space

C. The code causes a compile error

D. A heart-shaped custom character appears at the top-left corner

Solution

1. Step 1: Understand createChar and write usage

   The code defines a heart pattern, stores it at position 0, then writes character 0 at cursor (0,0).

2. Step 2: Predict LCD output

   Writing byte(0) displays the custom character stored at position 0, which is the heart shape.

3. Final Answer:

   A heart-shaped custom character appears at the top-left corner -> Option D

4. Quick Check:

   createChar + write(byte(0)) = custom char display [OK]

Hint: write(byte(0)) prints custom char stored at 0 [OK]

Common Mistakes:

• Expecting numeric 0 to print
• Forgetting to use byte() cast in write()
• Assuming createChar prints automatically

4. Identify the error in this code snippet for displaying a custom character:

byte star[8] = {4,14,21,4,4,0,4,0};
lcd.createChar(1, star);
lcd.setCursor(0,0);
lcd.write(1);

medium

A. Missing byte cast in lcd.write(1)

B. Array size is incorrect

C. createChar index must be 0, not 1

D. setCursor parameters are invalid

Solution

1. Step 1: Check usage of lcd.write()

   When writing a custom character, the index must be cast to byte, so lcd.write(byte(1)) is correct.

2. Step 2: Verify other parts

   Array size is 8, createChar index 1 is valid (0-7), setCursor(0,0) is valid.

3. Final Answer:

   Missing byte cast in lcd.write(1) -> Option A

4. Quick Check:

   Use byte() cast in write() for custom chars [OK]

Hint: Always cast index with byte() in lcd.write() [OK]

Common Mistakes:

• Not casting index to byte in lcd.write()
• Thinking createChar index must be zero
• Assuming setCursor(0,0) is invalid

5. You want to display two different custom characters side by side on the LCD. Which sequence correctly creates and displays them?

hard

A. Define two byte arrays, use createChar(1, char1) and createChar(2, char2), then write(1) and write(2).

B. Define one byte array with 16 elements, use createChar(0, array), then write(0) twice.

C. Define two byte arrays, use createChar(0, char1) and createChar(1, char2), then write(byte(0)) and write(byte(1)) in order.

D. Use createChar(0, char1) twice, then write(0) and write(1).

Solution

1. Step 1: Understand createChar indexing

   Custom characters are stored in slots 0 to 7. To display two different chars, use two slots, e.g., 0 and 1.

2. Step 2: Display characters correctly

   Use write(byte(0)) and write(byte(1)) to print the two custom characters side by side.

3. Final Answer:

   Define two byte arrays, use createChar(0, char1) and createChar(1, char2), then write(byte(0)) and write(byte(1)) in order. -> Option C

4. Quick Check:

   Two createChar slots + write(byte(index)) = display two chars [OK]

Hint: Use slots 0 and 1, write with byte() cast [OK]

Common Mistakes:

• Trying to store both chars in one array
• Using invalid createChar indexes like 2 or higher without checking
• Not casting index to byte in write()