Oh well, after hooking up my 4x20 LCD (that was held over from the Beagle Bone AI project, that I could never get to work) it still failed on my Arduino Mega. I ordered one, off eBay. The first thing I  did was to run the test program. Vola it worked.

The next piece of business was to get a formatted text to the display. Now as we all know Arduino does not support the C library function printf, which will sends formatted text to the console. Using printf is straight forward with these conventions:  int  printf( const *format, ......) here is it used to print the ASCII table

printf("ASCII value = %d, Character =%c\n", ch, ch ); you will note that the return int is optional.

But the Arduino you can't send the message to the LCD display without doing this. My function displayWrite( int row, char[] ) handles writing to either the LCD (during testing) or the LED displays. Furthermore, I can also wrap my library #include statements.


sprintf( line, "TANK #%d - %d", tank, lbs );
displayWrite ( 2, 0, line);


void dispalyWrite( int row, int col,  char[] ) {

        lcd.setCursor( col, row );

        lcd.print( line ); }


Since I will only be using the LCD for testing and a pair of HDSP-2131 (HDSP-2111) LED Display 5x7 8 characters that are part of the fuel display, and I don't want to rip my code when I change displays. Let me introduce a neat feature of the C preprocessor which are #ifdef, #ifndef, #elseif, #elif, #else, #endif.   I use them so I don't have to rewrite my display function ie. over the years I have gotten into the habit of writing modularized code. The star of the show is #ifdef. This directive works by looking at the term after the directive. If that term has not been #defined it will pass over this code block until an  #else, #endif is encountered.  Here is a nice reference on the #directives.


#define displayLCD

#ifdef displayLCD

#include <LiquidCrystal_I2C.h>

#include <Wire.h>



void dispalyWrite( int row, int col, char[] ) {

#ifdef displayLCD

        lcd.setCursor( col, row );

        lcd.print( line );


/// Code to drive the HDSP-2111 w/o shift reg


} // this closes the function.