I2C Character Display

This Rust embedded-hal-based library is a simple way to control a HD44780 compatible character display with an "I2C backpack" interface in an embedded, no_std environment. A number of I2C adapter interfaces are supported:

• Adafruit I2C/SPI LCD Backpack - This is a simple I2C backpack that can be used with either I2C or SPI. It is available from Adafruit and other retailers. This library only supports the I2C interface.
• PCF8574-based I2C adapter - These adapters are ubiquitous on eBay and AliExpress and have no clear branding. Furthermore, some character display makers, such as Surenoo, integrate a PCF8574T directly on the display board enabling I2C connections without a seperate adapter. The most common pin wiring uses 4 data pins and 3 control pins. Most models have the display 4-bit data pins connected to P4-P7 of the PCF8574. This library supports that configuration, though it would be straightforward to add support for other configurations.

Key features include:

• Convenient high-level API for controlling the display
• Support for custom characters
• Backlight control
• core::fmt::Write implementation for easy use with the write! macro
• Compatible with the embedded-hal traits v1.0 and later
• Support for character displays that uses multiple HD44780 drivers, such as the 40x4 display
• Optional support for the defmt and ufmt logging frameworks
• Optional support for reading from the display on adapters that support it

Usage

Add this to your Cargo.toml:

[dependencies]
i2c-character-display = { version = "0.1", features = ["defmt"] }

The features = ["defmt"] line is optional and enables the defmt feature, which allows the library's errors to be used with the defmt logging framework. Another optional feature is features = ["ufmt"], which enables the ufmt feature, allowing the uwriteln! and uwrite! macros to be used.

Then select the appropriate adapter for your display:

use i2c_character_display::{AdafruitLCDBackpack, CharacterDisplayPCF8574T, LcdDisplayType};
use embedded_hal::delay::DelayMs;
use embedded_hal::i2c::I2c;

// board setup
let i2c = ...; // I2C peripheral
let delay = ...; // DelayMs implementation

// It is recommended that the `i2c` object be wrapped in an `embedded_hal_bus::i2c::CriticalSectionDevice` so that it can be shared between
// multiple peripherals.

// Adafruit backpack
let mut lcd = AdafruitLCDBackpack::new(i2c, LcdDisplayType::Lcd16x2, delay);
// PCF8574T adapter
let mut lcd = CharacterDisplayPCF8574T::new(i2c, LcdDisplayType::Lcd16x2, delay);
// Character display with dual HD44780 drivers using a single PCF8574T I2C adapter
let mut lcd = CharacterDisplayDualHD44780::new(i2c, LcdDisplayType::Lcd40x4, delay);

When creating the display object, you can choose the display type from the LcdDisplayType enum. The display type should match the physical display you are using. This display type configures the number of rows and columns, and the internal row offsets for the display.

Initialize the display:

if let Err(e) = lcd.init() {
   panic!("Error initializing LCD: {}", e);
}

Use the display:

// set up the display
lcd.backlight(true)?.clear()?.home()?;
// print a message
lcd.print("Hello, world!")?;
// can also use the `core::fmt::write!` macro
use core::fmt::Write;

write!(lcd, "Hello, world!")?;

The optional ufmt feature enables the ufmt crate, which allows the uwriteln! and uwrite! macros to be used with the display:

use ufmt::uwriteln;

uwriteln!(lcd, "Hello, world!")?;

The various methods for controlling the LCD are also available. Each returns a Result that wraps the display object in Ok(), allowing for easy chaining of commands. For example:

lcd.backlight(true)?.clear()?.home()?.print("Hello, world!")?;

Reading from the display

Some I2C adapters support reading data from the HD44780 controller. Dor the I2C adapters that support it, the read_device_data method can be used to read from either the CGRAM or DDRAM at the current cursor position. The read_address_counter method can be used to read the address counter from the HD44780 controller. In both cases, the specific meaning of the data depends on the prior commands sent to the display. See the HD44780 datasheet for more information.

Multiple HD44780 controller character displays

Some character displays, such as the 40x4 display, use two HD44780 controllers to drive the display. This library supports these displays by treating them as one logical display with multiple HD44780 controllers. The CharacterDisplayDualHD44780 type is used to control these displays. Use the various methods to control the display as you would with a single HD44780 controller display. The set_cursor method sets the active HD44780 conmtroller device based on the row number you select.

License

Licensed under the MIT license.