philipgiuliani / lcd_display

Use character liquid crystal display (LCD) in Elixir

LcdDisplay

LcdDisplay allows you to control a Hitachi HD44780-compatible Liquid-crystal display (LCD) in Elixir.

For the specification of the HD44780 LCD, please refer to the HD44780 data sheet.

Installation

You can install LcdDisplay by adding lcd_display to your list of dependencies in mix.exs:

def deps do
  [
    {:lcd_display, "~> 0.2.0"}
  ]
end

Usage

As an example, if you want to control a Hitachi HD44780 type display through the 8-bit I/O expander PCF8574, you can use LcdDisplay.HD44780.PCF8574 module as a display driver.

Start an LCD driver and get a PID

driver_config = %{
  driver_module: LcdDisplay.HD44780.PCF8574,
  i2c_bus: "i2c-1",          # I2C bus name
  i2c_address: 0x27,         # 7-bit address
  rows: 2,                   # the number of display rows
  cols: 16,                  # the number of display columns
  font_size: "5x8"           # "5x10" or "5x8"
}

{:ok, pid} = LcdDisplay.start_link(driver_config)

Many configuration values are optional, falling back to default values. Please refer to each display module documentation.

Run commands

Please refer to the LcdDisplay.HD44780.Driver documentation for supported display commands.

# Print text
LcdDisplay.execute(pid, {:print, "Hello world"})

# Clear the display
LcdDisplay.execute(pid, :clear)

# Print a character at a time
LcdDisplay.execute(pid, {:print, 0b00110001})
LcdDisplay.execute(pid, {:print, 0b00110000})
LcdDisplay.execute(pid, {:print, 0b00100101})

Driver modules

Different products out there use different I/O expanders, so please be aware of which I/O expander you are using if you use something like an I2C backpack. Also the pin assignment between the LCD and the I/O expander is important since this library assumes certain pin assignment based on popular products out there.

for parallel I/O

When you connect an LCD standalone directly to the GPIO pins on your target device, the LcdDisplay.HD44780.GPIO driver module is useful.

Here are some relevant products:

• Adafruit Assembled Standard LCD 16x2 - White on Blue
• Adafruit Standard LCD 16x2 - white on blue
• Adafruit Standard LCD 20x4 - white on blue
• Adafruit RGB backlight LCD 16x2 - black on RGB
• Adafruit RGB backlight LCD 16x2 - RGB on black

for PCF8574-based I2C modules

Many inexpensive I2C modules on Amazon.com uses PCF8574. A pre-assembled 16x2 LCD with I2C module is typically less than US$10. Handson Technology I2C Serial Interface 1602 LCD Module User Guide summarizes the typical specifications of the PCF8574-based I2C module.

for Adafruit I2C / SPI character LCD backpack

The Adafruit i2c / SPI character LCD backpack supports both I2C and SPI interfaces. It uses MCP23008 for I2C and SN74HC595 for SPI as of writing.

for other I/O expanders

It is easy to make your own driver modules in case you want a custom pin assignment, a different I/O expander or some custom features.

Thanks

• ExLCD for inspiration