After 1602 LCD is powered on, why only the blue background is displayed instead of the program? There is nothing wrong with my program, even the yellow cursor is not displayed.
See if your RS, WR and EN pins are connected to the wrong port of the single chip microcomputer. I just got the wrong connection. I checked the N transformer circuit and asked my classmates to check it. Also, it may be welded. Use a multimeter to see if there are any welds. Take a good look at your diagram or program, it is easy to make mistakes.