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Python code for talking to HD44780 compatible character based dot matrix LCDs.

This code is synchronous. Peter Hinch put together an async driver forthe HD77480 overhere.

This library is based off of a C version that I wrote, which can be foundhere(also look for files in the same directory which start with lcd).

Nic created a C# port of this library which can be foundhere.

You can communicate with the LCDs using either 4 or 8 GPIO pins.

Alternatively, the I2C classes implement 8-bit GPIO expander boardsPCF8574 andMCP23008which reduces the number of required GPIO pins to two (SCL, SDA).The boards usually mount behind the LCDs and are commonly called "backpacks".

The most commonly used display is a "1602" or "16x2", which features 16 columnsand 2 rows of characters. There are also other LCDs using the same HD44780controller. eg. 8x2, 16x1, 16x4, 20x2, 20x4, 40x1, 40x2. Each come in variousbacklight and pixel colours.

There are also variants of the code forMicroPython.All of the files which start withpyb_ were tested on thepyboard.Files starting withesp8266_ were tested on aWeMos D1 Mini.Files starting withnodemcu_ were tested on aNodeMCU development board.The files containingadafruit_lcd were tested on an AdafruitI2C / SPI character LCD backpack

# python smbus needs dev headerssudo apt updatesudo apt install python3-devpython -m pip install smbus  # optional, good test before installing librarypython -m pip install -e .

# python smbus needs dev headerssudo apt updatesudo apt install python2-devpython -m pip install smbus  # optional, good test before installing librarypython -m pip install -e .

Giuseppe Cassibba wrote up atutorial which demonstrates connecting an I2C LCD to a Raspberry Pi Pico.

The files which end in_test.py are examples which show how the correspondingfile is used.

i2c_lcd.py was tested on aBeagleBone Black using a 2 x 16 LCD with an I2Cmodule similar tothis one.

To install on your BBB:

git clone https://github.com/dhylands/python_lcd.gitcd python_lcdsudo pip install -e.

And to test:

sudo lcd/i2c_lcd_test.py

Since my LCD was a 5v device, I used a level converter to convert from BBB's3.3v to the LCD's 5v.

I put together some[photos here] (https://picasaweb.google.com/115853040635737241756/PythonI2CLCD?authkey=Gv1sRgCLyZoJ3_uPjiXA)

Coming from the BeagleBone Black the wire colors are:

The photo shows Orange connected to P9-5. I discovered that P9-7 is controlledby the onboard voltage regulators, so when you do a "sudo poweroff" thenSYS_5V drops to 0v when the BBB is powered off. P9-5 (VDD_5V) remains at5v after the BBB is powered off.

And the colors going to the LCD are:

I used aSparkFun level shifter(this particular model is no longer available).

Some examples of other level shifters which could be used:

• Logic Level Converter
• Logic Level Converter Bi-Directional
• Voltage-Level Translator - TXB0104 Breakout
• PCA9306 Level Translator Breakout
• 4-channel I2C-safe Bi-directional Logic Level Converter - BSS138
• 8-channel Bi-directional Logic Level Converter - TXB0108

I found a circuit mentioned inthis Google+ postand thought I would include it here, since it's related to the LCDs these drivers interface with.

The circuit allows for digitally controlling the contrast via PWM and also controllingthe backlight brightness via PWM.

The HD44780 displays come with 3 possible CGROM font sets. Japanese, European and Custom.Test which you have using:

lcd.putchar(chr(247))

If you see Pi (π), you have a Japanese A00 ROM.If you see a division sign (÷), you have a European A02 ROM.

Characters match ASCII characters in range 32-127 (0x20-0x7F) with a few exceptions:

• 0x5C is a Yen symbol instead of backslash
• 0x7E is a right arrow instead of tilde
• 0x7F is a left arrow instead of delete

Only the ASCII characters are common between the two ROMs 32-125 (0x20-0x7D)Refer to the HD44780 datasheet for the table of characters.

The first 8 characters are CGRAM or character-generator RAM.You can specify any pattern for these characters.

To design a custom character, start by drawing a 5x8 grid.I use dots and hashes as it's a lot easier to read than 1s and 0s.Draw pixels by replacing dots with hashes.Where possible, leave the bottom row unpopulated as it may be occupied by the underline cursor.

Happy Face (where .=0, #=1)......#.#........#.......#...#.###......

To convert this into a bytearray for the custom_char() method, you need to add each row of 5 pixels to least significant bits of a byte (the right side).

Happy Face (where .=0, #=1)..... == 0b00000 == 0x00.#.#. == 0b01010 == 0x0A..... == 0b00000 == 0x00..#.. == 0b00100 == 0x04..... == 0b00000 == 0x00#...# == 0b10001 == 0x11.###. == 0b01110 == 0x0E..... == 0b00000 == 0x00

Next, add each byte from top to bottom to a new byte array and pass to custom_char() with location 0-7.

happy_face = bytearray([0x00,0x0A,0x00,0x04,0x00,0x11,0x0E,0x00])lcd.custom_char(0, happy_face)

custom_char() does not print anything to the display. It only updates the CGRAM.To display the custom characters, use putchar() with chr(0) through chr(7).

lcd.putchar(chr(0))lcd.putchar(b'\x00')

Characters are displayed by reference.Once you have printed a custom character to the lcd, you can overwrite the custom character and all visible instances will also update.This is useful for drawing animations and graphs, as you only need to print the characters once and then can simply modify the custom characters in CGRAM.

Examples:

# smiley faceshappy = bytearray([0x00,0x0A,0x00,0x04,0x00,0x11,0x0E,0x00])sad = bytearray([0x00,0x0A,0x00,0x04,0x00,0x0E,0x11,0x00])grin = bytearray([0x00,0x00,0x0A,0x00,0x1F,0x11,0x0E,0x00])shock = bytearray([0x0A,0x00,0x04,0x00,0x0E,0x11,0x11,0x0E])meh = bytearray([0x00,0x0A,0x00,0x04,0x00,0x1F,0x00,0x00])angry = bytearray([0x11,0x0A,0x11,0x04,0x00,0x0E,0x11,0x00])tongue = bytearray([0x00,0x0A,0x00,0x04,0x00,0x1F,0x05,0x02])# iconsbell = bytearray([0x04,0x0e,0x0e,0x0e,0x1f,0x00,0x04,0x00])note = bytearray([0x02,0x03,0x02,0x0e,0x1e,0x0c,0x00,0x00])clock = bytearray([0x00,0x0e,0x15,0x17,0x11,0x0e,0x00,0x00])heart = bytearray([0x00,0x0a,0x1f,0x1f,0x0e,0x04,0x00,0x00])duck = bytearray([0x00,0x0c,0x1d,0x0f,0x0f,0x06,0x00,0x00])check = bytearray([0x00,0x01,0x03,0x16,0x1c,0x08,0x00,0x00])cross = bytearray([0x00,0x1b,0x0e,0x04,0x0e,0x1b,0x00,0x00])retarrow = bytearray([0x01,0x01,0x05,0x09,0x1f,0x08,0x04,0x00])# battery iconsbattery0 = bytearray([0x0E,0x1B,0x11,0x11,0x11,0x11,0x11,0x1F])  # 0% Emptybattery1 = bytearray([0x0E,0x1B,0x11,0x11,0x11,0x11,0x1F,0x1F])  # 16%battery2 = bytearray([0x0E,0x1B,0x11,0x11,0x11,0x1F,0x1F,0x1F])  # 33%battery3 = bytearray([0x0E,0x1B,0x11,0x11,0x1F,0x1F,0x1F,0x1F])  # 50%battery4 = bytearray([0x0E,0x1B,0x11,0x1F,0x1F,0x1F,0x1F,0x1F])  # 66%battery5 = bytearray([0x0E,0x1B,0x1F,0x1F,0x1F,0x1F,0x1F,0x1F])  # 83%battery6 = bytearray([0x0E,0x1F,0x1F,0x1F,0x1F,0x1F,0x1F,0x1F])  # 100% Fullbattery7 = bytearray([0x0E,0x1F,0x1B,0x1B,0x1B,0x1F,0x1B,0x1F])  # ! Error

An online editor for creating customer characters is available online athttps://clach04.github.io/lcdchargen/ (source code available fromhttps://github.com/clach04/lcdchargen/tree/python)