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1. Driver for character-based LCD displays

This driver is for displays based on the Hitachi HD44780 driver: these are widely available, typically in 16 character x 2 rows format. This version is for asyncio V3 which requires firmware V1.13 or above; at the time of writing this has not been released and a daily build is required.

Main README

2. Files

The driver and test program are implemented as a Python package. To install copy the directory as_drivers/hd44780 and contents to the target's filesystem.

Files:

  • alcd.py Driver, includes connection details.
  • alcdtest.py Test/demo script.

To run the demo issue:

import as_drivers.hd44780.alcdtest

3. Typical wiring

The driver uses 4-bit mode to economise on pins and wiring. Pins are arbitrary but this configuration was used in testing:

LCD Board
Rs Y1
E Y2
D7 Y3
D6 Y4
D5 Y5
D4 Y6

4. LCD Class

4.1 Constructor

This takes the following positional args:

  • pinlist A tuple of 6 strings, being the Pyboard pins used for signals Rs, E, D4, D5, D6, D7 e.g. ('Y1','Y2','Y6','Y5','Y4','Y3').
  • cols The number of horizontal characters in the display (typically 16).
  • rows Default 2. Number of rows in the display.

The driver uses the machine library. For non-Pyboard targets with numeric pin ID's pinlist should be a tuple of integers.

4.2 Display updates

The class has no public properties or methods. The display is represented as an array of strings indexed by row. The row contents is replaced in its entirety, replacing all previous contents regardless of length. This is illustrated by the test program:

import asyncio
import utime as time
from as_drivers.hd44780 import LCD, PINLIST

lcd = LCD(PINLIST, cols = 16)

async def lcd_task():
    for secs in range(20, -1, -1):
        lcd[0] = 'MicroPython {}'.format(secs)
        lcd[1] = "{:11d}uS".format(time.ticks_us())
        await asyncio.sleep(1)

asyncio.run(lcd_task())

The row contents may be read back by issuing

row0 = lcd[0]

5. Display Formatting

The driver represents an LCD display as an array indexed by row. Assigning a string to a row causes that row to be updated. To write text to a specific column of the display it is recommended to use the Python string format method.

For example this function formats a string such that it is left-padded with spaces to a given column and right-padded to the specified width (typically the width of the display). Right padding is not necessary but is included to illustrate how right-justified formatting can be achieved:

def print_at(st, col, width=16):
    return '{:>{col}s}{:{t}s}'.format(st,'', col=col+len(st), t = width-(col+len(st)))
>>> print_at('cat', 2)
'  cat           '
>>> len(_)
16
>>>

This use of the format method may be extended to achieve more complex tabulated data layouts.