It's easy to use the IS31FL3731 Charlieplex breakout, the Charlieplex FeatherWing, and the CharliePlex Bonnet with Python or CircuitPython and the Adafruit CircuitPython IS31FL3731 module. This module allows you to easily write Python code that does all sorts of fun things with the LED matrix.
You can use CharliePlex LED matrices with any CircuitPython microcontroller board or with a computer that has GPIO and Python thanks to Adafruit_Blinka, our CircuitPython-for-Python compatibility library.
CircuitPython Microcontroller Wiring
First wire up a IS31FL3731 breakout to your board exactly as shown on the previous pages for Arduino.
For the FeatherWing, solder on the headers, and attach to the Feather.
Here is the CharlieWing on a Feather M4:
- Assemble the CharlieWing by soldering headers onto the board.
- Once assembled, plug it into a Feather!
Here's an example of wiring a Feather to the breakout with I2C:
- Board 3V to breakout VCC
- Board GND to breakout GND
- Board SCL to breakout SCL
- Board SDA to breakout SDA
Python Computer Wiring
Since there's dozens of Linux computers/boards you can use we will show wiring for Raspberry Pi. For other platforms, please visit the guide for CircuitPython on Linux to see whether your platform is supported.
For the Bonnet, simply attach the Bonnet to your Raspberry Pi header.
Here is the CharliePlex Bonnet on a Raspberry Pi Zero:
Here's the Raspberry Pi wired to the breakout with I2C:
Python Installation of IS31FL3731 Library
You'll need to install the Adafruit_Blinka library that provides the CircuitPython support in Python. This may also require enabling I2C on your platform and verifying you are running Python 3. Since each platform is a little different, and Linux changes often, please visit the CircuitPython on Linux guide to get your computer ready!
Once that's done, from your command line run the following command:
sudo pip3 install adafruit-circuitpython-is31fl3731 adafruit-circuitpython-framebuf
If your default Python is version 3 you may need to run 'pip' instead. Just make sure you aren't trying to use CircuitPython on Python 2.x, it isn't supported!
CircuitPython Installation of IS31FL3731 Library
You'll need to install the Adafruit CircuitPython IS31FL3731 library, and its dependencies, into the lib folder on your CIRCUITPY drive. Then you need to update code.py with the example script.
Thankfully, we can do this in one go. In the example below, click the Download Project Bundle button below to download the necessary libraries and the code.py file in a zip file. Extract the contents of the zip file, and copy the entire lib folder and the code.py file to your CIRCUITPY drive.
Your CIRCUITPY/lib folder should contain the following folders:
- /adafruit_is31fl3731
- /adafruit_bus_device
# SPDX-FileCopyrightText: 2021 ladyada for Adafruit Industries
# SPDX-License-Identifier: MIT
import board
import busio
# uncomment next line if you are using Feather CharlieWing LED 15 x 7
from adafruit_is31fl3731.charlie_wing import CharlieWing as Display
# uncomment next line if you are using Adafruit 16x9 Charlieplexed PWM LED Matrix
# from adafruit_is31fl3731.matrix import Matrix as Display
# uncomment next line if you are using Adafruit 16x8 Charlieplexed Bonnet
# from adafruit_is31fl3731.charlie_bonnet import CharlieBonnet as Display
# uncomment next line if you are using Pimoroni Scroll Phat HD LED 17 x 7
# from adafruit_is31fl3731.scroll_phat_hd import ScrollPhatHD as Display
# uncomment next line if you are using Pimoroni 11x7 LED Matrix Breakout
# from adafruit_is31fl3731.matrix_11x7 import Matrix11x7 as Display
# uncomment this line if you use a Pico, here with SCL=GP21 and SDA=GP20.
# i2c = busio.I2C(board.GP21, board.GP20)
i2c = busio.I2C(board.SCL, board.SDA)
display = Display(i2c)
# draw a box on the display
# first draw the top and bottom edges
for x in range(display.width):
display.pixel(x, 0, 50)
display.pixel(x, display.height - 1, 50)
# now draw the left and right edges
for y in range(display.height):
display.pixel(0, y, 50)
display.pixel(display.width - 1, y, 50)
CircuitPython & Python Usage
To demonstrate the usage of the sensor we'll initialize it and manipulate the LED matrix from the board's Python REPL.
To do this, connect to the board's serial REPL so you are at the CircuitPython >>> prompt.
NOTE: Due to size and design of each CharliePlex matrix form-factor, import and initialisation is different for each. Make sure you're running the correct code for your matrix!
First, run the following code to import the necessary modules:
import board import busio
If you're using the CharliePlex breakout, initialise it by running the following code:
from adafruit_is31fl3731.matrix import Matrix as Display
If you're using the CharliePlex FeatherWing, run the following code:
from adafruit_is31fl3731.charlie_wing import CharlieWing as Display
If you're using the CharliePlex Bonnet, run the following code:
from adafruit_is31fl3731.charlie_bonnet import CharlieBonnet as Display
Now, no matter which board you are using, you'll create the I2C object and pass that into Display.
i2c = busio.I2C(board.SCL, board.SDA) display = Display(i2c)
When the display initializes it will go through and clear each frame (there are 8 frames total) of the display. You might see the display momentarily flash and then turn off to a clear no pixel lit image.
You can control all of the board's pixels using the fill function. Send to this function a value from 0 to 255 where 0 is every LED pixel turned off and 255 is every LED pixel turned on to maximum brightness. For example to set all the pixels to half their brightness run:
display.fill(127)
You might notice some buzzing or ringing sounds from the display when all pixels are lit, this is normal as the Charlieplex driver quickly switches LEDs on and off.
If you've used other displays like LED matrices you might notice the Charlieplex module doesn't need to have a show function called to make the changes visible. As soon as you call fill or other display functions the display will update!
You can turn all the pixels off with fill set to 0:
display.fill(0)
Now for some fun! You can set any of the LED pixels using the pixel function. This function takes the following parameters:
- X position - The location of the horizontal / X pixel position.
- Y position - The location of the vertical / Y pixel position.
-
Intensity - This is a value from
0to255which specifies how bright the pixel should be, 0 is off and 255 is maximum brightness. Use an in-between value to show a less bright pixel.
For example to set pixel 0, 0 to full brightness run:
display.pixel(0, 0, 255)
Or to set the pixel next to it horizontally to half brightness run:
display.pixel(1, 0, 127)
You can turn off individual pixels by setting them to an intensity of zero.
You can even make pixels blink! The board supports a fixed blink rate that you set using the blink function. This function takes in the number of milliseconds to use for the blink rate (but internally it can only blink in 270ms increments so you might not get an exact match). For example to blink pixels about once every half second call:
display.blink(500)
You'll notice nothing actually changes on the board. This is because in addition to intensity each LED pixel has a blink state which can be enabled and disabled. The fill command can actually set all pixels and turn them on to blink:
display.fill(127, blink=True)
You can turn off the blinking by setting blink=False.
The pixel command supports the blink parameter too! You can turn on and off blinking pixel by pixel as needed. For example to turn on blinking for pixel 0, 0:
display.pixel(0, 0, 127, blink=True)
Currently the Charlieplex module is very simple and only exposes pixel set commands. In the future more advanced graphics commands like line drawing, text display, etc. might be implemented but for now you'll need to manipulate the pixels yourself.
Finally the display supports holding up to 8 frames of pixel data. Each frame contains an entire matrix of LED pixel state (intensity, blinking, etc.) and by default the module starts you on frame 0. You can change to start displaying and drawing on another frame by calling frame which takes these parameters:
-
Frame number - This is the frame number to make the active frame for display or drawing. There are 8 frames total,
0through7. -
show- An optional boolean that defaults toTrueand specifies if the frame should be immediately displayed (True) or just made active so that pixel and fill commands draw on it but it's not yet shown.
For example to clear frame 1 and draw a few pixels on it, then display it you can run:
display.frame(1, show=False) display.fill(0) display.pixel(0, 0, 255) display.pixel(1, 1, 255) display.pixel(2, 2, 255) display.frame(1) # show=True is the default, the frame will be displayed!
Notice how the first call switches to make frame 1 the active frame but doesn't display it because show is set to false. Then the frame pixel data is changed with fill and pixel commands, and finally the frame is shown by calling frame again but letting the default show = True be used so the frame is displayed.
Using frames you can build simple animations by drawing each frame and swapping between them over time!
That's all there is to the basic Charlieplex driver module usage!
Text Scrolling Example
NOTE: When running this example on Raspberry Pi, you must have the font8x5.bin file found here in the same directory as the program!
wget https://raw.githubusercontent.com/adafruit/Adafruit_CircuitPython_framebuf/master/examples/font5x8.bin
# SPDX-FileCopyrightText: 2021 ladyada for Adafruit Industries
# SPDX-License-Identifier: MIT
import adafruit_framebuf
import board
import busio
# uncomment next line if you are using Feather CharlieWing LED 15 x 7
# from adafruit_is31fl3731.charlie_wing import CharlieWing as Display
# uncomment next line if you are using Adafruit 16x9 Charlieplexed PWM LED Matrix
# from adafruit_is31fl3731.matrix import Matrix as Display
# uncomment next line if you are using Adafruit 16x8 Charlieplexed Bonnet
from adafruit_is31fl3731.charlie_bonnet import CharlieBonnet as Display
# uncomment next line if you are using Pimoroni Scroll Phat HD LED 17 x 7
# from adafruit_is31fl3731.scroll_phat_hd import ScrollPhatHD as Display
# uncomment next line if you are using Pimoroni 11x7 LED Matrix Breakout
# from adafruit_is31fl3731.matrix_11x7 import Matrix11x7 as Display
# uncomment this line if you use a Pico, here with SCL=GP21 and SDA=GP20.
# i2c = busio.I2C(board.GP21, board.GP20)
i2c = busio.I2C(board.SCL, board.SDA)
display = Display(i2c)
text_to_show = "Adafruit!!"
# Create a framebuffer for our display
buf = bytearray(32) # 2 bytes tall x 16 wide = 32 bytes (9 bits is 2 bytes)
fb = adafruit_framebuf.FrameBuffer(buf, display.width, display.height, adafruit_framebuf.MVLSB)
frame = 0 # start with frame 0
while True:
for i in range(len(text_to_show) * 9):
fb.fill(0)
fb.text(text_to_show, -i + display.width, 0, color=1)
# to improve the display flicker we can use two frame
# fill the next frame with scrolling text, then
# show it.
display.frame(frame, show=False)
# turn all LEDs off
display.fill(0)
for x in range(display.width):
# using the FrameBuffer text result
bite = buf[x]
for y in range(display.height):
bit = 1 << y & bite
# if bit > 0 then set the pixel brightness
if bit:
display.pixel(x, y, 50)
# now that the frame is filled, show it.
display.frame(frame, show=True)
frame = 0 if frame else 1
Page last edited January 22, 2025
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