pyLCD

A library for controlling LCDs on various hardware backends


Keywords
library lcd display hd44780 ks0108 interface
License
AGPL-3.0
Install
pip install pyLCD==1.1.3

Documentation

pyLCD – A library for controlling LCDs on various hardware backends

The instructions and tips below are for HD44780 compatible character LCDs. Using KS0108 compatible graphical LCDs is basically the same, only with different pin names and function names.

License

This program is licensed under the AGPLv3. See the LICENSE file for more information.

Installation

You can easily install the pyLCD lib using the Python Package Index. Just type:

sudo pip install pylcd

Hardware support

This library supports multiple hardware platforms for input and output.

Currently available output backends:

  • Velleman K8055 USB Experiment Interface Board
  • Raspberry Pi GPIO pins
  • Arduino pins using serial communication (Still in development)
  • Debug output showing the states of the interface pins
  • Dummy output that does nothing

Currently available input backends:

  • System standard input (e.g. Keyboard)
  • Raspberry Pi GPIO pins
  • No input

See the usage examples below for examples on how to use them.

Output pinmaps

When instantiating a display, you need to pass it a dictionary containing a mapping from pin names on the LCD to output numbers on the device you're connecting the LCD to. For a K8055, you might want to use this pinmap:

PINMAP = {
    'RS': 1,
    'RW': 2,
    'E': 3,
    'D4': 4,
    'D5': 5,
    'D6': 6,
    'D7': 7,
    'LED': 9,
}

Note that the backlight LED pin is numbered 9 here, even though the K8055 only has 8 digital outputs. But since there are two additional analog outputs, I numbered them 9 and 10 to avoid confusion. Using an analog output for backlight control enables you to dim the backlight by using PWM!

For a Raspberry Pi, you need to use WiringPi's WPI_MODE_GPIO pin numbering scheme. I connected my LCD as follows:

PINMAP = {
    'RS': 2,
    'RW': 3,
    'E': 4,
    'D4': 22,
    'D5': 10,
    'D6': 9,
    'D7': 11,
    'LED': 18,
}

By using pin 18 for the backlight control, it's once again possible to dim the backlight since this pin is the only available hardware PWM pin of the Pi, so I recommend using this one. If you are using the DebugBackend backend, the pin numbers don't matter.

Input pinmaps

If you are using an input module that uses I/O pins, you need to specify a pinmap for that module as well. Currently, only five keys are supported: Up, Left, OK, Right and Down, as well as two LEDs: Ready and Error. My pinmap looks like this:

INPUT_PINMAP = {
    'UP': 23,
    'LEFT': 7,
    'OK': 8,
    'RIGHT': 24,
    'DOWN': 25,
    'READY': 27,
    'ERROR': 22,
}

Character maps

You can also specify a character map to use for defining custom characters. This is a dictionary in the following format:

CHARMAP = {
    0: (
        0b10101,
        0b01010,
        0b10101,
        0b01010,
        0b10101,
        0b01010,
        0b10101,
        0b01010,
    ),
}

The keys should be integers from 0 to 7, since the HD44780 can store up to 8 custom characters. The values should be tuples or lists of 8 integers, where each integer represents a line of the custom character. I recommend writing these integers in binary notation, since it's easy to see which pixels will be active and which won't if you do it this way.

You can also specify a single key, dir, to load custom characters from image files:

CHARMAP = {
    'dir': "/path/to/directory",
}

The specified directory should contain up to 8 image files (preferably in PNG format) numbered 0.<suffix> to 7.<suffix>. Each of these files must be 5 pixels wide and 8 pixels tall and should consist of black and white pixels, where a black pixel will translate into an active pixel on the display. To use this feature, you need to have the Python Imaging Library (PIL) installed.

User Interface

This library comes with a DisplayUI class which allows you to create simple text-based user interfaces with just a few lines of code! See the usage examples below. Have a look at the lcd.py file to see what is possible.

Usage examples

To initialize a standard 16x2 character LCD with a blinking cursor on a Raspberry Pi, you would do:

import hd44780
PINMAP = {} # Your pinmap here
display = hd44780.Display(backend = hd44780.GPIOBackend, pinmap = PINMAP, lines = 2, columns = 16)
display.set_display_enable(cursor = True, cursor_blink = True)
display.clear()
display.home()

To display a Yes / No dialog and react to the user's choice on said display, using physical keys attached to the Pi, do the following:

INPUT_PINMAP = {} # Your pinmap here
ui = hd44780.DisplayUI(display, hd44780.GPIOInput, input_kwargs = {'pinmap': INPUT_PINMAP})
selected_index, selected_text = ui.dialog("Proceed?", buttons = ("Yes", "No"))
if selected_index == 0:
    ui.message("Doing stuff...")
else:
    ui.message("Aborted.")

Note that if you are using the SystemInput input backend you need to be able to send keypresses to the terminal running the script, or else it won't be able to react to your input. For more examples I would suggest looking at the included example scripts.