GEMMA M0 boards can run CircuitPython — a different approach to programming compared to Arduino sketches. In fact, CircuitPython comes factory pre-loaded on GEMMA M0. If you’ve overwritten it with an Arduino sketch, or just want to learn the basics of setting up and using CircuitPython, this is explained in the Adafruit GEMMA M0 guide.

These directions are specific to the “M0” GEMMA board. The original GEMMA with an 8-bit AVR microcontroller doesn’t run CircuitPython…for those boards, use the Arduino sketch on the prior page of this guide.

Below is CircuitPython code that works similarly to the Arduino sketch shown on a prior page. To use this, plug the GEMMA M0 into USB…it should show up on your computer as a small flash drive…then edit the file “” with your text editor of choice. Select and copy the code below and paste it into that file, entirely replacing its contents (don’t mix it in with lingering bits of old code). When you save the file, the code should start running almost immediately (if not, see notes at the bottom of this page).

If GEMMA M0 doesn’t show up as a drive, follow the GEMMA M0 guide link above to prepare the board for CircuitPython.

# SPDX-FileCopyrightText: 2017 Phillip Burgess for Adafruit Industries
# SPDX-License-Identifier: MIT

import board
import neopixel

    import urandom as random  # for v1.0 API support
except ImportError:
    import random

numpix = 17  # Number of NeoPixels
pixpin = board.D1  # Pin where NeoPixels are connected
strip = neopixel.NeoPixel(pixpin, numpix)

minAlpha = 0.1  # Minimum brightness
maxAlpha = 0.4  # Maximum brightness
alpha = (minAlpha + maxAlpha) / 2  # Start in middle
alphaDelta = 0.008  # Amount to change brightness each time through loop
alphaUp = True  # If True, brightness increasing, else decreasing

strip.fill([255, 0, 0])  # Fill red, or change to R,G,B of your liking

while True:  # Loop forever...
    if random.randint(1, 5) == 5:  # 1-in-5 random chance
        alphaUp = not alphaUp  # of reversing direction
    if alphaUp:  # Increasing brightness?
        alpha += alphaDelta  # Add some amount
        if alpha >= maxAlpha:  # At or above max?
            alpha = maxAlpha  # Limit to max
            alphaUp = False  # and switch direction
    else:  # Else decreasing brightness
        alpha -= alphaDelta  # Subtract some amount
        if alpha <= minAlpha:  # At or below min?
            alpha = minAlpha  # Limit to min
            alphaUp = True  # and switch direction

    strip.brightness = alpha  # Set brightness to 0.0 to 1.0
    strip.write()  # and issue data to LED strip

This code requires the library. A factory-fresh board will have this already installed. If you’ve just reloaded the board with CircuitPython, create the “lib” directory and then download from Github.

This guide was first published on Oct 07, 2015. It was last updated on Apr 20, 2024.

This page (CircuitPython Code) was last updated on Apr 20, 2024.

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