lcd

Hitachi HD44780 LCD driver

npm install lcd
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lcd

A Node.js Hitachi HD44780 LCD driver for Linux boards such as the BeagleBone or Raspberry Pi. Heavily inspired by the Arduino LiquidCrystal library.

Most LCDs compatible with the HD44780 have a sixteen pin interface. This Node.js module uses six of these interface pins for controlling such displays. Register select (RS), enable (E), and four data bus pins (D4-D7). The read/write (R/W) pin is assumed to be tied low to permanently select write mode.

Installation

$ [sudo] npm install lcd

lcd requires Node.js v0.8.0 or higher.

Usage

The following nine line program can be used to make a digital clock.

var Lcd = require('lcd'),
  lcd = new Lcd({rs:27, e:65, data:[23, 26, 46, 47], cols:8, rows:1});

lcd.on('ready', function () {
  setInterval(function () {
    lcd.setCursor(0, 0);
    lcd.print(new Date().toISOString().substring(11, 19));
  }, 1000);
});

Here it is up and running on a BeagleBone Black wired up to an 8x1 display:

After requiring the lcd module, the above program creates an Lcd object. The constructor function is passed all the necessary information.

The six LCD interface pins used to control the display need to be wired up to six GPIOs on the BeagleBone Black. GPIOs on Linux are identified by unsigned integers. The relevant information for all six GPIOs used here is shown in the following table:

BBB Expansion Header GPIO No. LCD Function LCD Pin No.
P8_13 23 Data Bus Bit 4 11
P8_14 26 Data Bus Bit 5 12
P8_15 47 Data Bus Bit 7 14
P8_16 46 Data Bus Bit 6 13
P8_17 27 Register Select 4
P8_18 65 Enable 6

The constructor function is also told how many columns and rows the display has, eight and one respectively in this case.

It takes several milliseconds to initialize an LCD. The constructor starts the initialization process, but it doesn't wait for it to complete. Instead, a 'ready' event is emitted after the LCD has been completely initialized and is ready for usage.

The 'ready' handler leverages setInterval to execute a function that updates the time displayed on the LCD once a second.

Adding the following few lines will turn the digital clock into a good citizen that cleans up after itself.

// If ctrl+c is hit, free resources and exit.
process.on('SIGINT', function () {
  lcd.close();
  process.exit();
});

News & Updates

lcd v0.2.0 breaking asynchronous print change

As of lcd v0.2.0 the print method is asynchronous. In previous versions it was synchronous.

API

Lcd(config)

Returns a new Lcd object which inherits from EventEmitter. A 'ready' event will be emitted when the display is ready for usage.

The config object has these possibilities:

  • cols LCD column count. Defaults to sixteen.
  • rows LCD row count. Defaults to one.
  • largeFont Use 5x10 dot font. Defaults to false for 5x8 dot font.
  • rs Register select GPIO number.
  • e Enable GPIO number.
  • data Array of four GPIO numbers for data bus bits D4 through D7.

print(val) Converts val to string and write it to the display asynchronously. A 'printed' event is emitted after the operation has completed. val is passed to the event handler as the first argument. The example print-twice-20x4.js demonstrates how to print two strings in succession.

clear() Clears display and returns cursor to the home position. A 'clear' event is emitted after the operation has completed.

home() Returns cursor to home position. Also returns display being shifted to the original position. A 'home' event is emitted after the operation has completed.

setCursor(col, row) Moves the cursor to the specified col and row. Numbering for col and row starts at zero.

cursor() Turn cursor on.

noCursor() Turn cursor off.

blink() Turn cursor blink on.

noBlink() Turn cursor blink off.

scrollDisplayLeft() Shift display to the left. Cursor follows the display shift.

scrollDisplayRight() Shift display to the right. Cursor follows the display shift.

leftToRight() Sets cursor move direction to left to right.

rightToLeft() Sets cursor move direction to right to left.

autoscroll() Automatically shift display when data is written to display.

noAutoscroll() Turn automatic shifting off.

close() Frees (unexports) all GPIOs used by the Lcd.

Example "Hello, World!" on an 8x1 display

"Hello, World!" is five characters too long for an 8x1 display, but by moving the cursor to the ninth column, turning autoscroll on, and displaying a new character every 300 milliseconds the text can be scrolled onto the display character by character. Note that an 8x1 display actually has eighty columns but only eight of them are visible.

var Lcd = require('../lcd'),
  lcd = new Lcd({rs:27, e:65, data:[23, 26, 46, 47], cols:8, rows:1});

lcd.on('ready', function () {
  lcd.setCursor(8, 0);
  lcd.autoscroll();
  print('Hello, World! ** ');
});

function print(str, pos) {
  pos = pos || 0;

  if (pos === str.length) {
    pos = 0;
  }

  lcd.print(str[pos]);

  setTimeout(function () {
    print(str, pos + 1);
  }, 300);
}

Tested with the following displays

NHD-0108FZ-FL-YBW-33V3

NHD-0420DZ-FL-YBW-33V3

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