Issues With Escaping Characters in PROGMEM

Using Arduino Programming Questions
#1

Hello!
I have been having issues writing strings from PROGMEM to a character LCD directly using the F() macro.

There are two issues I am having escaping characters:

  • On this lcd, you can program your own characters (up to 8 ). These characters are stored as characters 0 through 8, represented by hex 0x00 - 0x08. To print these characters, you just escape those hex codes in a string (eg. “Hi!\x00”). The problem I’m having here is that escaping \x00 (null) in a PROGMEM string acts as a terminator, ending the printed string prematurely!
    –Edit: Solved, just use the duplicate characters stored on the LCD memory, 0x08-0x15! (still declare them as 0 through 8)

  • Using an escaped character as the first character of a string (null or otherwise) results in some weirdness, including lost characters and left-shifting(see image, tried to print the string shown in code)

#include <LiquidCrystal.h>
#include <avr/pgmspace.h>

const byte chars[8][8]={
  {
    0b00000,
    0b00100,
    0b00110,
    0b11111,
    0b00110,
    0b00100,
    0b00000,
    0b00000
  },
  {
    0b00000,
    0b00100,
    0b01100,
    0b11111,
    0b01100,
    0b00100,
    0b00000,
    0b00000
  }
};

LiquidCrystal lcd(16,17,23,25,27,29);
long lastUpdate=0;

void setup(){
  lcd.begin(20,4);
  lcd.createChar(2,chars[0]);
  lcd.createChar(1,chars[1]);
  
  lcd.clear();
}
void loop(){
  if(millis()-lastUpdate<500)return;
  lastUpdate=millis();
  lcd.setCursor(0,0);

  lcd.print(F("\x01Back               \x02Speed              \x02Pattern            \x02Setup              "));

}

This code works, however, if you replace the first “\x01” with a space or other character…

:slight_smile:

SAM_0218 DOWNSIZED.jpg
SAM_0218 DOWNSIZED.jpg960×540 88 KB

#2

You can't put character 0 in a string without terminating it. Try using .write() for the binary values.

  lcd.write(1);
  lcd.print(F("Back               "));
  lcd.write(2);
  lcd.print(F("Speed              "));
  lcd.write(2);
  lcd.print(F("Pattern            "));

  lcd.write(2);

  lcd.print(F("Setup              "));
#3

Hi johnwasser!
Thanks for your reply.
However, is there a way to decrease the compile size of this? Using so many lcd methods takes a lot of memory and time, so that's why I only used one call to the function...

#4