Python code for talking to HD44780 compatible character based dot matrix LCDs.
You can communicate with the LCDs using either 4 or 8 GPIO pins.
Alternatively, the I2C classes implement 8-bit GPIO expander boards PCF8574 and MCP23008 which 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 columns and 2 rows of characters. There are also other LCDs using the same HD44780 controller. eg. 8x2, 16x1, 16x4, 20x2, 20x4, 40x1, 40x2. Each come in various backlight and pixel colours.
There are also variants of the code for MicroPython. All of the files which start with pyb_ were tested on the pyboard. Files starting with esp8266_ were tested on a WeMos D1 Mini. Files starting with nodemcu_ were tested on a NodeMCU development board. The files containing adafruit_lcd were tested on an Adafruit I2C / SPI character LCD backpack
| File | Description |
|---|---|
| esp8266_i2c_lcd.py | ESP8266 PCF8574 I2C HAL |
| esp8266_i2c_lcd_test.py | ESP8266 test using PCF8574 backpack |
| i2c_lcd.pyb | Linux PCF8574 I2C HAL |
| i2c_lcd_test.pyb | Linux test using PCF8574 backpack |
| lcd.py | Core logic |
| nodemcu_gpio_lcd.py | NodeMCU GPIO HAL |
| nodemcu_gpio_lcd_test.py | NodeMCU test using 4-bit GPIO |
| pyb_gpio_lcd.py | Pyboard GPIO HAL |
| pyb_gpio_lcd_test8.py | Pyboard test using 8-bit GPIO |
| pyb_gpio_lcd_test.py | Pyboard test using 4-bit GPIO |
| pyb_i2c_adafruit_lcd.py | Pyboard MCP23008 I2C HAL |
| pyb_i2c_adafruit_lcd_test.py | Pyboard test using Adafruit backpack |
| pyb_i2c_lcd.py | Pyboard PCF8574 I2C HAL |
| pyb_i2c_lcd_test.py | Pyboard test using PCF8574 backpack |
The files which end in _test.py are examples which show how the corresponding file is used.
i2c_lcd.py was tested on a BeagleBone Black using a 2 x 16 LCD with an I2C module similar to this one.
This code was adapted from some C code that I had written previously for the AVR.
To install on your BBB:
git clone https://github.com/dhylands/python_lcd.git
cd python_lcd
sudo pip install -e .And to test:
sudo lcd/i2c_lcd.pySince my LCD was a 5v device, I used a level converter to convert from BBB's 3.3v 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:
Color Pin Name
------ ----- ------
Black P9-1 GND
Red P9-3 3.3v
Orange P9-7 SYS_5V
Yellow P9-19 SCL
White P9-20 SDA
The photo shows Orange connected to P9-5. I discovered that P9-7 is controlled by the onboard voltage regulators, so when you do a "sudo poweroff" then SYS_5V drops to 0v when the BBB is powered off. P9-5 (VDD_5V) remains at 5v after the BBB is powered off.
And the colors going to the LCD are:
Color Name
------ ----
Black GND
Red 5v
White SDA
Yellow SCL
I used a SparkFun 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 in this Google+ post
and 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 controlling the backlight brightness via PWM.