Power-electronicsHow-ToBeginner · 4 min read

How to Display Custom Character on LCD in Embedded C

To display a custom character on an LCD in embedded C, define the character pattern as a byte array and load it into the LCD's CGRAM using lcd_create_char() or equivalent function. Then, display it by writing the custom character's code to the LCD with lcd_write() or similar.

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Syntax

To display a custom character on an LCD, you typically follow these steps:

Define the character pattern as an array of bytes, each byte representing a row of pixels.
Load this pattern into the LCD's CGRAM (Character Generator RAM) using a function like lcd_create_char(location, pattern).
Display the custom character by writing its location code (0-7) to the LCD using lcd_write(location).

Each byte in the pattern usually has 5 bits for pixels (for a 5x8 LCD character).

embedded_c

uint8_t customChar[8] = {
  0b00000,
  0b01010,
  0b10101,
  0b10001,
  0b10101,
  0b01010,
  0b00000,
  0b00000
};

lcd_create_char(0, customChar); // Load pattern into CGRAM location 0
lcd_set_cursor(0, 0);          // Set cursor to first row, first column
lcd_write(0);                  // Display custom char stored at location 0

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Example

This example shows how to define a smiley face custom character, load it into the LCD, and display it at the first position.

embedded_c

#include <stdint.h>
#include "lcd.h"  // Assume lcd.h provides lcd_create_char, lcd_set_cursor, lcd_write

int main() {
    uint8_t smiley[8] = {
        0b00000,
        0b01010,
        0b01010,
        0b00000,
        0b10001,
        0b01110,
        0b00000,
        0b00000
    };

    lcd_init();               // Initialize LCD
    lcd_create_char(0, smiley); // Load smiley into CGRAM slot 0
    lcd_set_cursor(0, 0);    // Move cursor to first row, first column
    lcd_write(0);            // Display custom char at location 0

    while(1) {}
    return 0;
}

Output

Smiley face character displayed at first row, first column of the LCD

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Common Pitfalls

Not loading the custom character into CGRAM before displaying it causes blank or wrong characters.
Using a location outside 0-7 for CGRAM will not work because LCDs support only 8 custom chars.
Forgetting to set the cursor position before writing the character can display it in the wrong place.
Incorrect byte patterns can produce unexpected shapes; ensure each byte uses only the lower 5 bits for pixels.

embedded_c

/* Wrong: Using location 8 (invalid) */
lcd_create_char(8, customChar); // Invalid location, will not display

/* Right: Use location 0-7 */
lcd_create_char(0, customChar); // Correct usage

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Quick Reference

Step	Description
Define pattern	Create 8-byte array with 5-bit pixel rows
Load pattern	Use lcd_create_char(location, pattern) with location 0-7
Set cursor	Position cursor with lcd_set_cursor(row, col)
Display char	Write location code with lcd_write(location)

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Key Takeaways

Define your custom character as an 8-byte array with 5-bit pixel rows.

Load the character into LCD CGRAM at a location between 0 and 7 before displaying.

Set the LCD cursor to the desired position before writing the custom character code.

Only 8 custom characters can be stored at once on typical 16x2 or 20x4 LCDs.

Verify your byte patterns carefully to get the correct shape on the LCD.