Custom characters on LCD in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What does this Arduino LCD code output?

Consider this Arduino code snippet that creates a custom character and displays it on an LCD:

byte smiley[8] = {
  0b00000,
  0b01010,
  0b01010,
  0b00000,
  0b10001,
  0b01110,
  0b00000,
  0b00000
};

void setup() {
  lcd.begin(16, 2);
  lcd.createChar(0, smiley);
  lcd.setCursor(0, 0);
  lcd.write(byte(0));
}

void loop() {}

What will appear on the LCD screen?

Arduino

byte smiley[8] = {
  0b00000,
  0b01010,
  0b01010,
  0b00000,
  0b10001,
  0b01110,
  0b00000,
  0b00000
};

void setup() {
  lcd.begin(16, 2);
  lcd.createChar(0, smiley);
  lcd.setCursor(0, 0);
  lcd.write(byte(0));
}

void loop() {}

A Compilation error due to incorrect byte array size

B The LCD shows a blank space at the first position

C The LCD displays a random character at the first position

D A smiling face icon appears at the first position on the LCD

💡 Hint

Custom characters are stored in CGRAM and displayed by writing their index as a byte.

The createChar function stores the custom pattern in CGRAM slot 0. Writing byte(0) prints that custom character, which looks like a smiling face.

🧠 Conceptual

intermediate

How many custom characters can an Arduino LCD typically store?

When using the LiquidCrystal library on a standard 16x2 LCD, how many custom characters can you create and store at the same time?

A 8 custom characters

B 16 custom characters

C 4 custom characters

D 32 custom characters

💡 Hint

Think about the CGRAM memory size in HD44780 compatible LCDs.

Standard HD44780 LCD controllers have 64 bytes of CGRAM, enough for 8 characters of 8 bytes each.

🔧 Debug

advanced

Why does this custom character not display correctly?

Look at this Arduino code snippet:

byte heart[7] = {
  0b00000,
  0b01010,
  0b11111,
  0b11111,
  0b11111,
  0b01110,
  0b00100
};

void setup() {
  lcd.begin(16, 2);
  lcd.createChar(1, heart);
  lcd.setCursor(0, 0);
  lcd.write(byte(1));
}

void loop() {}

The heart shape does not appear as expected on the LCD. What is the most likely cause?

A The LCD is not initialized with <code>lcd.begin</code>

B The <code>lcd.write</code> function cannot print custom characters

C The byte array has only 7 rows instead of 8, causing incorrect display

D The <code>createChar</code> index 1 is invalid; it must be 0

💡 Hint

Custom characters require exactly 8 bytes for 8 rows.

The custom character array must have 8 bytes, one for each row. Missing one row causes the LCD to display garbage or nothing.

📝 Syntax

advanced

Which option correctly defines a custom character array for LCD?

Choose the correct syntax to define a custom character pattern for an Arduino LCD:

A byte customChar[8] = {0b00000, 0b01010, 0b10101, 0b01010, 0b00000, 0b00000, 0b00000, 0b00000};

B byte customChar[8] = (0b00000, 0b01010, 0b10101, 0b01010, 0b00000, 0b00000, 0b00000, 0b00000);

C byte customChar[7] = {0b00000, 0b01010, 0b10101, 0b01010, 0b00000, 0b00000, 0b00000};

D byte customChar = {0b00000, 0b01010, 0b10101, 0b01010, 0b00000, 0b00000, 0b00000, 0b00000};

💡 Hint

Remember how to declare arrays in Arduino (C++).

Option A correctly declares an array of 8 bytes with curly braces. Option A misses the array size, C has only 7 elements, and D uses parentheses instead of braces.

🚀 Application

expert

How to display multiple custom characters on LCD simultaneously?

You want to display two different custom characters side by side on a 16x2 LCD using Arduino. You have created two custom characters at indexes 0 and 1. Which code snippet correctly displays both characters on the first row?

A lcd.setCursor(0, 0); lcd.write(0); lcd.write(1);

B lcd.setCursor(0, 0); lcd.write(byte(0)); lcd.write(byte(1));

C lcd.setCursor(0, 0); lcd.print(byte(0)); lcd.print(byte(1));

D lcd.setCursor(0, 0); lcd.print(0); lcd.print(1);

💡 Hint

Use write to print custom characters by their byte index.

The lcd.write(byte(n)) function prints the custom character stored at index n. Using print with byte values prints their ASCII codes, not custom characters.

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()