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 GEMMA v2 with an 8-bit AVR microcontroller doesn’t run CircuitPython…for those boards, use the Arduino sketch on the “Arduino code” page of this guide.

Below is CircuitPython code that works similarly (though not exactly the same) as 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: 2018 Mikey Sklar for Adafruit Industries
# SPDX-License-Identifier: MIT

import board
import neopixel
import adafruit_fancyled.adafruit_fancyled as fancy

num_leds = 16       # number of LEDs per strip
saturation = 255    # 0-255, 0 is pure white, 255 is fully saturated color
blend = True        # color blending between palette indices
brightness = 0.8    # brightness the range is 0.0 - 1.0
flicker = 0          # flame flicker

# NeoPixel objects using
leds = neopixel.NeoPixel(board.D0, num_leds)

# Inspired by Fire2012() by Mark Kriegsman and his use of FastLED
# to create a one-dimensional 'fire' simulation
# the heat colors are from the heat palette that FastLED provides
def fire_2018(strip, offset):
    # heat colors
    palette = [0x330000, 0x660000, 0x990000, 0xCC0000, 0xFF0000,
               0xFF3300, 0xFF6600, 0xFF9900, 0xFFCC00, 0xFFFF00,
               0xFFFF33, 0xFFFF66, 0xFFFF99, 0xFFFFCC]

    for i in range(num_leds):
        # FancyLED can handle the gamma adjustment, brightness and RGB settings
        color = fancy.palette_lookup(palette, offset + i / num_leds)
        color = fancy.gamma_adjust(color, brightness=brightness)
        strip[i] = color.pack()

while True:
    fire_2018(leds, flicker)
    flicker += 0.3           # flame flicker, adjust value to control speed

Installing Libraries

This code requires two libraries be installed:

  • neopixel
  • adafruit_fancyled

 A factory-fresh board will have the neopixel library already installed. If you’ve just reloaded the board with CircuitPython, create the “lib” directory and then copy in the neopixel.mpy and adafruit_fancyled folder from the latest release of the Adafruit_CircuitPython_Bundle

The FancyLED library being using in this CircuitPython example is not the same as the FastLEDused for Arduino. FancyLED has a subset of FastLED features and some different syntax. The FancyLED tutorial provides an excellent overview

The file system layout on your gemma M0 should look like this:

$ pwd
$ find .

This guide was first published on Dec 22, 2015. It was last updated on Jun 17, 2024.

This page (CircuitPython Code) was last updated on Jun 17, 2024.

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