LCD not displaying text

Question

I am working with an Arduino due and currently using the Arduino liquid crystal library to display data on an LCD screen (mc42004A6wk-bnmlw) which uses the Hitachi HD44780 controller. The LCD has been update to v2 and is now using the Sitronix ST7066U controller.

From what I have read the two controllers are compatible and the liquid crystal library should work for both. I am using the same software and hardware setup as before but the screen will not display anything.

The software I use is quite complex so I moved to a simple hello world program (below) to test and I still have the same issues. Any advice would be greatly appreciated.

#include <LiquidCrystal.h>
#include <Arduino.h>

LiquidCrystal lcd(30, 31, 32, 33, 46, 47);

void setup() 
{

  pinMode(36,OUTPUT);

  digitalWrite(36, LOW);

  delay(5000);

  // set up the LCD's number of columns and rows:
  lcd.begin(20, 4);

  lcd.clear();

  // Print a message to the LCD.
  lcd.print("hello, world!");
}

void loop() 
{

  delay(5000);
  // set the cursor to column 0, line 1
  // (note: line 1 is the second row, since counting begins with 0):
  lcd.setCursor(0, 1);
  // print the number of seconds since reset:
  lcd.print(millis() / 1000);
}

Answer 1

Try using this code, I have edited some parts of your code so this should work.

#include <LiquidCrystal.h>

const int rs = 30, en = 31, d4 = 32, d5 = 33, d6 = 46, d7 = 47;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

void setup()
{

  pinMode(36, OUTPUT);
  digitalWrite(36, LOW);
  delay(5000);    //Its okay to use delay here since its in the setup() function and will run only once

  // set up the LCD's number of columns and rows:
  lcd.begin(20, 4);

  // Print a message to the LCD.
  lcd.print("hello, world!");
}

void loop()
{
  // set the cursor to column 0, line 1
  // (note: line 1 is the second row, since counting begins with 0):
  lcd.setCursor(0, 1);
  // print the number of seconds since reset:
  lcd.print(millis() / 1000);
}

For this Hello World sketch, avoid using delay(); statement in the void loop() as it is not good to use when you have the millis(); used.

If the above wont work, check your LCD Wiring, many problems usually arouse from wrong wirings. Also I may suggest you to use some cheap LCD I2C Backpacks as this will ease the coding and will use less wire and pins on your Arduino. Here is a example

If your'e going to use a I2C LCD Backpack, here is a working sample code.

#include <Wire.h> 
#include <LiquidCrystal_I2C.h>

#define BACKLIGHT_PIN     13

LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE); // Set the LCD I2C address

// Creat a set of new characters
const uint8_t charBitmap[][8] = {
   { 0xc, 0x12, 0x12, 0xc, 0, 0, 0, 0 },
   { 0x6, 0x9, 0x9, 0x6, 0, 0, 0, 0 },
   { 0x0, 0x6, 0x9, 0x9, 0x6, 0, 0, 0x0 },
   { 0x0, 0xc, 0x12, 0x12, 0xc, 0, 0, 0x0 },
   { 0x0, 0x0, 0xc, 0x12, 0x12, 0xc, 0, 0x0 },
   { 0x0, 0x0, 0x6, 0x9, 0x9, 0x6, 0, 0x0 },
   { 0x0, 0x0, 0x0, 0x6, 0x9, 0x9, 0x6, 0x0 },
   { 0x0, 0x0, 0x0, 0xc, 0x12, 0x12, 0xc, 0x0 }

};

void setup()
{
   int charBitmapSize = (sizeof(charBitmap ) / sizeof (charBitmap[0]));

  // Switch on the backlight
  pinMode ( BACKLIGHT_PIN, OUTPUT );
  digitalWrite ( BACKLIGHT_PIN, HIGH );

  //lcd.begin(16,2); 
  lcd.begin(20,4); // initialize the lcd 

   for ( int i = 0; i < charBitmapSize; i++ )
   {
      lcd.createChar ( i, (uint8_t *)charBitmap[i] );
   }

  lcd.home ();                   // go home
  lcd.print("LCD TESTER - BY:");  
  lcd.setCursor ( 0, 1 );        // go to the next line
  lcd.print ("ABBAS (PRJCT.ME)");
  delay ( 3000 );
}

void loop()
{
   lcd.home ();
   // Do a little animation by writing to the same location
   //for ( int i = 0; i < 2; i++ )
    for ( int i = 0; i < 4; i++ )
   {
      //for ( int j = 0; j < 16; j++ )
      for ( int j = 0; j < 20; j++ )
      {
         lcd.print (char(random(7)));
      }
      lcd.setCursor ( 0, 1 );
       for ( int j = 0; j < 20; j++ )
      {
         lcd.print (char(random(7)));
      }
      lcd.setCursor ( 0, 2 );
       for ( int j = 0; j < 20; j++ )
      {
         lcd.print (char(random(7)));
      }
      lcd.setCursor ( 0, 3 );

   }
   delay (200);
}

Answer 2

So after further investigation into the IDE, Libraries, board manager, hardware etc I discovered what was causing the issue.

On the initial hardware design the hardware engineer placed a capacitor on the enable leg between the LCD screen and the microcontroller. I have no idea why as I have not seen this done in any wiring diagrams but removing it has done the trick. The V2 board now works with all the original code and libraries.