Weird problem with specific pixels in LCD createChar

Using Arduino Programming Questions
1

Hi,
I've been trying to debug my code to print custom characters in 16X2 LCD, and after a day of work trying to compare to the smiley example (which works) with my code, I pinpointed the problem to one pixel.

I started changing bit by bit of the first row, from 0 to 1, compiling every time, until the smiley stopped printing.
The culprit is bit[1] of the top row in smiley definition. Make it 0, it all compiles and and a smiley is printed. Make it 1 and it compiles but nothing is printed.
Below is the full code. I don't have another LCD module to test. Can anyone reproduce the problem?

Thanks.

#include <LiquidCrystal.h>

LiquidCrystal lcd(12, 11, 5, 4, 3, 2); // RS, E, D4, D5, D6, D7

 byte smiley[8] = {
  B11101,
  B10001,
  B00000,
  B00000,
  B10001,
  B01110,
  B00000
};

void setup() { 
 
  lcd.createChar(0, smiley);
  lcd.setCursor(3, 2);
  lcd.write(byte(0));

Change the smiley assignment to :

byte smiley[8] = {

  • B11111,*
  • B10001,*
  • B00000,*
  • B00000,*
  • B10001,*
  • B01110,*
  • B00000*
    };

and it stops printing.

2

What happens if you use 0b00011101 and 0b00011111 instead of the #defined values ?

Please post a complete sketch that demonstrates the problem.

3

Why do you put only 7 bytes in your 8-byte array?

4

I took the examples as is from this Arduino site.
I didn't post the whole code because it's dirty with failed attempts commented out, but what I posted is the whole working code, except for the final closing bracket that I missed pasting.

5

Do you mean the CreateChar example?

#include <LiquidCrystal.h>

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

byte smiley[8] = {
 B00000,
 B10001,
 B00000,
 B00000,
 B10001,
 B01110,
 B00000,
};

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

void loop() {}

Note how the example has " lcd.begin(16, 2);" where you have " lcd.setCursor(3, 2);", which, by the way, is trying to display on the third line?!? Undo that change and you will find that it works much better.

6

Hi John,
thanks for your reply.
I eliminated the lcd.begin because it blanks the screen. I found it empirically but later found an explanation in the forum.
Set cursor (3,2) I think it's Position 3, line 2. Even if I'm wrong, I've tried all kind of positions.
After all the tests, I downed it to 1 bit (pixel), that if I set it, it doesn't print anything, and if clear it, the char is printed. Tried it many times and the behavior is consistent.
Anyway, I'm leaving this project because I think the 16X2 LCD is not the right HW to display different alphabets, and it's futile to "convince it" with SW tricks.
Thanks again for your help.
David.

7

Set cursor (3,2) I think it's Position 3, line 2

Correct, but you don't have a line 2 only lines 0 and 1