HD44780 based LCD display

In this example we are going to connect to HD44780 based LCD display.

The display I am using  has 2 lines with 16 letters each. Same example will also work for HD44780 based displays that have 4 lines with 20 letters per line.

For more specialized versions (custom sizes of the HD44780 then you can find information on those in part 2)

Pieces we use:

• Raspberry Pi 2, 3, 4 or 5.
• Cobbler and Cobbler cable.
• Breadbboard (I found it nice to use 2 for this example)
• Header pins to solder into the display. (If the display does not have pins)
• HD4478 based LCD display. I had 1602 LCD module with blue backlight
• 10 kΩ potentiometer.
• 560 Ω resistor.
  
  • Not required if you’re buying the LCD from Adafruit
  • Many displays do not have a current limiting resistor installed for the LED backlight, this resistor is only needed for those.  It is hard to tell until you actually apply power to the LCD if yours has built in resistor or not. So it is a good idea to put in a resistor to begin with at least.
  • This may vary between displays, I used 1 kΩ resistor, and the display was bright. 560 Ω is common though and probably would have been fine for me.
  
  
• Gpiod Plugin for Xojo to use libpgiod in Xojo. The plugin you can get download here.  Or if you are interested in its source code then you can go here.

Soldering:

Usually those displays do not come with pins soldered on them. So you can either solder header pins on it or wires. The displays take standard header pins with 2,54 mm spacing.

This is how it looked like after I quickly soldered the one I tested:

I opted for letting the pins come out at back so I can push the display into a breadboard, or later if I use the display in permanent project I can use the display in a case without the pins sticking out at front.

Connecting the LCD:

When connecting then its best to connect LCD pins 1, 2, 15 and 16 first as well as fully connecting the potentiometer (see connection map bellow).

Then turn on the Raspberry PI and adjust the potentiometer until you clearly see boxes outlining character placeholders in one of the lines in the display. If you are unable to get the placeholders, then re-check your connections.

Once you can see the placeholders clearly then you can power down your Raspberry Pi and proceed to connect the rest of the pins on the display.

Make sure that your Raspberry PI is not turned on when your wiring it up. 

The Xojo Code

This example uses whole screen driver class which you will find in the example project in Git. We will only post highlight here in the code since the code is a bit long.

Private Property mLCD As HD44780Display

And then Opening event for the Window:

Sub Opening() Handles Opening
  try
    using Gpiod
    
    var chip as Chip = Chip.Open("/dev/gpiochip0")
    
    Const kRSPin as UInt32 = 25
    Const kEPin as UInt32 = 24
    Const kD4Pin as UInt32 = 23
    Const kD5Pin as UInt32 = 17
    Const kD6Pin as UInt32 = 21
    Const kD7Pin as UInt32 = 22
    
    mLCD = new HD44780Display(chip, kRSPin, kEPin, kD4Pin, kD5Pin, kD6Pin, kD7Pin)
    
    var glyph as LCDGlyph
    
    // We create some glyph, the display can store max 8 at once, but we can set up as many as we want here since our code 
    // will apply them in smart way so that the limit will not be how many are set up but the limit will be 8 different custom 
    //glyphs per line in the display.
    
    // A Glyph that represents the Icelandic Thorn letter (upper case)
    glyph = new LCDGlyph
    glyph.SetLine(0,&b10000)
    glyph.SetLine(1,&b10000)
    glyph.SetLine(2,&b11100)
    glyph.SetLine(3,&b10010)
    glyph.SetLine(4,&b10010)
    glyph.SetLine(5,&b11100)
    glyph.SetLine(6,&b10000)
    glyph.SetLine(7,&b10000)
    
    glyph.LetterCode = Asc("Þ")
    
    mLCD.RegisterCustomGlyph(glyph)
    
    // A Glyph that represents the Icelandic Thorn letter (lower case)
    glyph = new LCDGlyph
    glyph.SetLine(0,&b10000)
    glyph.SetLine(1,&b10000)
    glyph.SetLine(2,&b11100)
    glyph.SetLine(3,&b10010)
    glyph.SetLine(4,&b10010)
    glyph.SetLine(5,&b10010)
    glyph.SetLine(6,&b11100)
    glyph.SetLine(7,&b10000)
    
    glyph.LetterCode = Asc("þ")
    
    mLCD.RegisterCustomGlyph(glyph)
    
    // A Glyph that represents the ó letter (lower case)
    glyph = new LCDGlyph
    glyph.SetLine(0,&b00010)
    glyph.SetLine(1,&b00100)
    glyph.SetLine(2,&b01110)
    glyph.SetLine(3,&b10001)
    glyph.SetLine(4,&b10001)
    glyph.SetLine(5,&b10001)
    glyph.SetLine(6,&b01110)
    glyph.SetLine(7,&b00000)
    
    glyph.LetterCode = Asc("ó")
    
    mLCD.RegisterCustomGlyph(glyph)
    
    
    // A Glyph that represents the ö letter (lower case)
    glyph = new LCDGlyph
    glyph.SetLine(0,&b01010)
    glyph.SetLine(1,&b00000)
    glyph.SetLine(2,&b01110)
    glyph.SetLine(3,&b10001)
    glyph.SetLine(4,&b10001)
    glyph.SetLine(5,&b10001)
    glyph.SetLine(6,&b01110)
    glyph.SetLine(7,&b00000)
    
    glyph.LetterCode = Asc("ö")
    
    mLCD.RegisterCustomGlyph(glyph)
    
    // A Glyph that represents the í letter (lower case)
    glyph = new LCDGlyph
    glyph.SetLine(0,&b00010)
    glyph.SetLine(1,&b00100)
    glyph.SetLine(2,&b00000)
    glyph.SetLine(3,&b01100)
    glyph.SetLine(4,&b00100)
    glyph.SetLine(5,&b00100)
    glyph.SetLine(6,&b01110)
    glyph.SetLine(7,&b00000)
    
    glyph.LetterCode = Asc("í")
    
    mLCD.RegisterCustomGlyph(glyph)
    
  catch e as GpiodException
    MessageBox(e.Message)
  end try
End Sub

Sending text to the display:

Sub Action() Handles Action
  try
    mLCD.Clear()
    mLCD.Home()
    mLCD.SetMessage(tbLine1.Text, 1,true)
    mLCD.SetMessage(tbLine2.Text, 2,true)
  catch ex as GpiodException
    MessageBox(ex.Message)
  end try
End Sub

And here are example results what the code generates, notice the Icelandic letters that the display should not support normally without custom glyphs:

The mask when setting up custom Glyphs is a Binary mask for each line that consists of 5 bits, and you have 8 lines.

So graphically setting up a glyph would look like this:

Which would give the following mask:

glyph = new GPIO.LCDGlyph
glyph.SetLine(0,&b00010)
glyph.SetLine(1,&b00100)
glyph.SetLine(2,&b00000)
glyph.SetLine(3,&b01100)
glyph.SetLine(4,&b00100)
glyph.SetLine(5,&b00100)
glyph.SetLine(6,&b01110)
glyph.SetLine(7,&b00000)