liquid_crystal

liquid crystal is a modular library for alphanumeric lcd displays compatible with the hd44780 controller, made in Rust with Embedded_hal API

How to use

first steps

First you must choose a display communication interface, this library provides two built-in interfaces, parallel and I2C (you can create your own interfaces see here )

then you must choose the number of bits in the communication, that can be: Bus4Bits or Bus8Bits

finally you must choose a Layout (you can create your own layout see here )

    let mut lcd_interface = Parallel::new(D4, D5, D6, D7, rs, en, en2);
    let mut lcd = LiquidCrystal::new(&mut interface, Bus4Bits, LCD16X2);

(Not all interfaces support 8Bit communication, but all interfaces that support 8Bit can support 4Bitn)

sending commands and text

(this may change in the future, see here )

first you must configure the display.

for this you must call the "begin" function. (you can configure directly with the low level "send" function, not recommended if you don't know how to configure the HD44780)

    lcd.begin(&mut delay);

you can send text and commands by the "write" function, this function receives a reference from a delay function and an Enum "SendType" which can be Text or Command

to send a text, pass a &str to the "Text" variant

to send a command, pass a command from the command list to the "Command" varient

    lcd.write(&mut delay,Command(Clear))
        .write(&mut delay,Text("hello World!"));

you can send custom characters to variant "CustomChar", but first you need to create your custom character by function "custom_char", this function receives delay like all others, a reference to an array of u8 with size 8, and the slot that he will occupy

• how does custom characters work?
• custom character generator

HD44780 allows you to create 8 custom characters (slot 0 - 7), you can create and modify these slots at any time, but only 8 different characters can be written at the same time on the display. (creating these characters returns the display to its initial position, then use "set_cursor" after creating these characters)

to send use the CustomChar variant with the character slot:

    let lightning: [u8; 8] = [0x03, 0x06, 0x0C, 0x1F, 0x1F, 0x03, 0x06, 0x0C];

    lcd.custom_char(&mut delay, &lightning, 0);
    lcd.write(&mut delay, CustomChar(0));

Exemple

exemple/stm32f1xx/hello.rs

#![no_std]
#![no_main]

use panic_halt as _;
use cortex_m_rt::entry;
use stm32f1xx_hal::{pac, prelude::*};
use liquid_crystal::{prelude::*};
use liquid_crystal::Parallel;

#[entry]
fn main() -> ! {

    //Rust logo
    let rust1: [u8; 8] = [0b00001,0b00011,0b00011,0b01110,0b11100,0b11000,0b01000,0b01000];
    let rust2: [u8; 8] = [0b10001,0b11111,0b00000,0b00000,0b11110,0b10001,0b10001,0b11110];
    let rust3: [u8; 8] = [0b10000,0b11000,0b11000,0b01110,0b00111,0b00011,0b00010,0b000010];

    let rust4: [u8; 8] = [0b01000,0b01000,0b11000,0b11100,0b01110,0b00011,0b00011,0b00001];
    let rust5: [u8; 8] = [0b11000,0b10100,0b10010,0b00000,0b00000,0b00000,0b11111,0b10001];
    let rust6: [u8; 8] = [0b00010,0b00010,0b00011,0b00111,0b01110,0b11000,0b11000,0b10000];

    let cp = cortex_m::Peripherals::take().unwrap();
    let dp = pac::Peripherals::take().unwrap();

    let mut flash = dp.FLASH.constrain();
    let rcc = dp.RCC.constrain();
    let clocks = rcc.cfgr.freeze(&mut flash.acr);


    let mut gpioc = dp.GPIOC.split();
    let mut gpioa = dp.GPIOA.split();


    let en = gpioc.pc13.into_push_pull_output(&mut gpioc.crh);
    let rs = gpioc.pc14.into_push_pull_output(&mut gpioc.crh);
    let d4 = gpioc.pc15.into_push_pull_output(&mut gpioc.crh);
    let d5 = gpioa.pa0.into_push_pull_output(&mut gpioa.crl);
    let d6 = gpioa.pa1.into_push_pull_output(&mut gpioa.crl);
    let d7 = gpioa.pa2.into_push_pull_output(&mut gpioa.crl);

    let mut delay = cp.SYST.delay(&clocks);

    let mut lcd_interface = Parallel::new(d4, d5, d6, d7, rs, en, lcd_dummy);
    let mut lcd = LiquidCrystal::new(&mut lcd_interface, Bus4Bits, LCD16X2);

    lcd.begin(&mut delay);
    lcd.custom_char(&mut delay, &rust1, 0);
    lcd.custom_char(&mut delay, &rust2, 1);
    lcd.custom_char(&mut delay, &rust3, 2);
    lcd.custom_char(&mut delay, &rust4, 3);
    lcd.custom_char(&mut delay, &rust5, 4);
    lcd.custom_char(&mut delay, &rust6, 5);

    lcd.write(&mut delay,Text("hello World!"))
        .write(&mut delay,Command(MoveLine2))
        .write(&mut delay,Text("made in Rust!"));
    lcd.set_cursor(&mut delay, 0, 13)
        .write(&mut delay, CustomChar(0))
        .write(&mut delay, CustomChar(1))
        .write(&mut delay, CustomChar(2));

    lcd.set_cursor(&mut delay, 1, 13)
        .write(&mut delay, CustomChar(3))
        .write(&mut delay, CustomChar(4))
        .write(&mut delay, CustomChar(5));
    loop {}
}

creating your own interface

to create your own interface, you must implement the "Interface" Trait which contains the "send" function

The "send" function receives two u8 parameters, "data" and "config", in which their Bits represent:

(still no function to read, so keep the R/W pin in pull down) (EN2corresponds to the display backlight in the I2C module)

where 0 and 1 represent the state of the pin 1: HIGH 0: LOW connect the bits to their respective ports, and congratulations you have created your own interface

(to work with PCF8574 you can copy this line let package = (config & 0b00000111) | (data & 0xF0) | 0x08; and send it through I2C library of your choice)

command list

Clear Clears the display

Reset resets the display's internal variables

ShiftCursotLeft Moves the cursor to the left

ShiftCursotRight Moves the cursor to the right

ShiftDisplayLeft Moves the display left

ShiftDisplayRight Moves the display right

MoveLine1 moves the cursor to the beginning of the first line of the controller

MoveLine2 moves the cursor to the beginning of the second line of the controller

configuration functions

echo enable all displays

select_lcd select a display (0 = EN1 | 1 = EN2)

enable_blink enable blinking cursor

enable_cursor enable cursor

enable_display enable display

enable_autoscroll enable autoscroll

disable_blink disable blinking cursor

disable_cursor disable cursor

disable_display disable display

disable_autoscroll disable autoscroll

set_autoscroll_increment autoscroll increments position

set_autoscroll_decrement autoscroll decrements position

update_config send the configs to the display

layouts

you can create custom layouts using the Layout struct.

creating custom layouts can be very useful if you want to create user interfaces using alphanumeric LCDs.

The HD44780 supports a total of 2 lines and up to 40 columns, each line has its address.

line 1 = 0x80 line 2 = 0xC0

many LCDs rearrange these lines and columns to change the Layout, for example:

for the 20X4 Display work, the 40 columns of each line are divided into 2 of 20, and to access it, it is necessary to use the line address + offset of 20, so the lines are organized like this:

Line 1 = 0x80 Line 2 = 0xC0 Line 3 = 0x80 + 20 Line 4 = 0xC0 + 20

you can create using struct Layout!

Layout receives two generic arguments COLUMNS and LINES, inside this struct there is an array of u8 and LINE size

each position represents a line in your Layout, just place the addresses following the example below:

const LCD16X2: Layout<16,2> = Layout{
    addrs: [0x80, 0xC0],
};

const LCD20X4: Layout<20,4> = Layout{
    addrs: [0x80, 0xC0, 0x80+20, 0xC0+20],
};

(note that you don't have to use all 40 columns if you don't want to)

why this API?

I use lcd display for a long time, and I always had to rewrite the Drive when I need to use some IO expander, because the current APIs don't provide a simple way to port the communication.

*this API is currently a personal test using embedded_hal, current syntax may change based on users feedback.