Python & CircuitPython

It's easy to use the Adafruit Trellis with Python or CircuitPython, and the Adafruit CircuitPython Trellis module. This module enables you to write Python code that allows you to easily control the LEDs and read button presses on a single Trellis board, or with a matrix of up to eight Trellis boards.

You can use this board 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 Trellis to your board exactly as shown on the previous pages for Arduino.  Here's an example of wiring a Feather M0 to the Trellis using I2C:

  • Board 3V to Trellis 5V/VCC
  • Board GND to Trellis GND
  • Board SCL to Trellis SCL
  • Board SDA to Trellis 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

Here's the Raspberry Pi wired to a Trellis:

  • Pi 5V to Trellis 5V
  • Pi GND to Trellis GND
  • Pi SCL to Trellis SCL
  • Pi SDA to Trellis SDA

CircuitPython Installation of Trellis Library

Next you'll need to install the Adafruit CircuitPython Trellis library on your CircuitPython board.  

First, make sure you are running the latest version of Adafruit CircuitPython for your board.

Next, you'll need to install the necessary libraries to use the hardware--carefully follow the steps to find and install these libraries from Adafruit's CircuitPython library bundle.  Our introduction guide has a great page on how to install the library bundle for both express and non-express boards.

Copy the following libraries from the bundle to the lib folder on your CIRCUITPY drive:

  • adafruit_trellis.mpy
  • adafruit_bus_device

Before continuing make sure your board's lib folder or root filesystem has the adafruit_trellis.mpy, and adafruit_bus_device files and folders copied over.

Next connect to the board's serial REPL so you are at the CircuitPython >>> prompt.

Python Installation of Trellis 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-trellis

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 & Python Usage

To demonstrate the usage of the Trellis, we'll initialize it, control the LEDs and read the button presses from the board's Python REPL.

Run the following code to import the necessary modules and initialize the I2C connection with the Trellis:

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import time
import busio
from board import SCL, SDA
from adafruit_trellis import Trellis

i2c = busio.I2C(SCL, SDA)
trellis = Trellis(i2c)

Now, you're ready to control the LEDs and read button presses with the following:

  • fill - Turns on all of the LEDs
  • brightness - Change the brightness of the LEDs
  • auto_show - When set to True, LED changes update automatically. When set to False, you must call show() to update the LEDs. Defaults to True.
  • show() - Required to update the LEDs if auto_show=False.
  • read_buttons - read the button matrix on the Trellis board. Returns two lists: one for button presses and one for button releases.

To turn on all the LEDs:

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trellis.led.fill(True)

To turn off all the LEDs:

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trellis.led.fill(False)

To read when the buttons are pressed and released:

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pressed_buttons = set()
while True:
    time.sleep(.1)
    just_pressed, released = trellis.read_buttons()
    for b in just_pressed:
        print('pressed:', b)
        trellis.led[b] = True
    pressed_buttons.update(just_pressed)
    for b in released:
        print('released:', b)
        trellis.led[b] = False
    pressed_buttons.difference_update(released)
    for b in pressed_buttons:
        print('still pressed:', b)
        trellis.led[b] = True

That's all there is to using your Trellis with CircuitPython!

Full Example Code

# Basic example of turning on LEDs and handling Keypad
# button activity.

# This example uses only one Trellis board, so all loops assume
# a maximum of 16 LEDs (0-15). For use with multiple Trellis boards,
# see the documentation.

import time
import busio
from board import SCL, SDA
from adafruit_trellis import Trellis

# Create the I2C interface
i2c = busio.I2C(SCL, SDA)

# Create a Trellis object
trellis = Trellis(i2c)  # 0x70 when no I2C address is supplied

# 'auto_show' defaults to 'True', so anytime LED states change,
# the changes are automatically sent to the Trellis board. If you
# set 'auto_show' to 'False', you will have to call the 'show()'
# method afterwards to send updates to the Trellis board.

# Turn on every LED
print('Turning all LEDs on...')
trellis.led.fill(True)
time.sleep(2)

# Turn off every LED
print('Turning all LEDs off...')
trellis.led.fill(False)
time.sleep(2)

# Turn on every LED, one at a time
print('Turning on each LED, one at a time...')
for i in range(16):
    trellis.led[i] = True
    time.sleep(.1)

# Turn off every LED, one at a time
print('Turning off each LED, one at a time...')
for i in range(15, 0, -1):
    trellis.led[i] = False
    time.sleep(.1)

# Now start reading button activity
# - When a button is depressed (just_pressed),
#   the LED for that button will turn on.
# - When the button is relased (released),
#   the LED will turn off.
# - Any button that is still depressed (pressed_buttons),
#   the LED will remain on.
print('Starting button sensory loop...')
pressed_buttons = set()
while True:
    # Make sure to take a break during each trellis.read_buttons
    # cycle.
    time.sleep(.1)

    just_pressed, released = trellis.read_buttons()
    for b in just_pressed:
        print('pressed:', b)
        trellis.led[b] = True
    pressed_buttons.update(just_pressed)
    for b in released:
        print('released:', b)
        trellis.led[b] = False
    pressed_buttons.difference_update(released)
    for b in pressed_buttons:
        print('still pressed:', b)
        trellis.led[b] = True
This guide was first published on Dec 06, 2013. It was last updated on Dec 06, 2013. This page (Python & CircuitPython) was last updated on Nov 16, 2019.