Custom characters on LCD in Arduino - Step-by-Step Execution

Concept Flow - Custom characters on LCD

Define 8-byte pattern array

↓

Create custom char in LCD memory

↓

Set cursor position on LCD

↓

Write custom char to LCD

↓

Display

The program defines a pattern for a custom character, loads it into the LCD's memory, sets the cursor, and then displays the custom character on the screen.

Execution Sample

Arduino

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

lcd.createChar(0, smiley);
lcd.setCursor(0, 0);
lcd.write(byte(0));

This code defines a smiley face pattern, loads it as custom char 0, moves cursor to top-left, and displays the smiley.

Execution Table

Step	Action	Variable/Function	Value/Effect	LCD State
1	Define custom char pattern	smiley	[0,10,0,0,17,14,0,0]	No change
2	Load custom char into LCD	lcd.createChar(0, smiley)	Custom char 0 stored	Custom char 0 memory updated
3	Set cursor position	lcd.setCursor(0, 0)	Cursor at col 0, row 0	Cursor moved
4	Write custom char	lcd.write(byte(0))	Displays custom char 0	Smiley shown at (0,0)
5	End	-	-	Program waits for next commands

💡 All steps completed, custom character displayed on LCD at position (0,0).

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
smiley	undefined	[0,10,0,0,17,14,0,0]	[0,10,0,0,17,14,0,0]	[0,10,0,0,17,14,0,0]	[0,10,0,0,17,14,0,0]	[0,10,0,0,17,14,0,0]
lcd custom char 0	empty	empty	loaded with smiley pattern	loaded with smiley pattern	loaded with smiley pattern	loaded with smiley pattern
cursor position	undefined	undefined	undefined	(0,0)	(0,0)	(0,0)
LCD display	blank	blank	blank	blank	smiley at (0,0)	smiley at (0,0)

Key Moments - 3 Insights

Why do we use lcd.createChar before lcd.write?

lcd.createChar loads the pattern into LCD memory so lcd.write can display it; without loading, lcd.write won't show the custom shape (see steps 2 and 4 in execution_table).

What does the byte array represent?

Each byte in the array defines one row of the 5x8 pixel character; bits set to 1 light pixels, 0 leave them off (step 1 in execution_table).

Why do we use byte(0) in lcd.write?

byte(0) tells lcd.write to display the custom character stored at position 0 in LCD memory (step 4 in execution_table).

Visual Quiz - 3 Questions

Look at the execution_table, what is the cursor position after step 3?

A (0,0)

B (1,0)

C (0,1)

D undefined

💡 Hint

Check the 'cursor position' value in variable_tracker after step 3.

At which step is the custom character pattern loaded into LCD memory?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column in execution_table for loading custom char.

If we change lcd.write(byte(0)) to lcd.write(byte(1)), what happens?

A Displays the smiley again

B Displays a different custom char if defined at 1

C Displays nothing

D Causes an error

💡 Hint

Custom chars are stored at positions 0-7; writing byte(1) shows char at position 1 if created.

Concept Snapshot

Custom characters on LCD:
- Define 8-byte array for 5x8 pixel pattern
- Use lcd.createChar(index, pattern) to load
- Set cursor with lcd.setCursor(col, row)
- Display with lcd.write(byte(index))
- LCD supports up to 8 custom chars (0-7)

Full Transcript

This example shows how to create and display a custom character on an LCD using Arduino. First, we define a byte array representing the pixel pattern of the character. Then, we load this pattern into the LCD's memory at a specific index using lcd.createChar. Next, we set the cursor position where we want to display the character. Finally, we write the custom character to the LCD using lcd.write with the index. The execution table traces each step, showing variable states and LCD changes. Key moments clarify why loading the character before writing is necessary, what the byte array means, and why we use byte(0) in lcd.write. The visual quiz tests understanding of cursor position, loading step, and what happens if we write a different custom char index. The snapshot summarizes the process in a quick reference format.