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 “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.

import adafruit_fancyled.adafruit_fancyled as fancy
import board
import neopixel
from digitalio import DigitalInOut, Direction, Pull

led_pin = board.D1  # which pin your pixels are connected to
num_leds = 78  # how many LEDs you have
brightness = 1.0  # 0-1, higher number is brighter
saturation = 255  # 0-255, 0 is pure white, 255 is fully saturated color
steps = 0.01  # how wide the bands of color are.
offset = 0  # cummulative steps
fadeup = True  # start with fading up - increase steps until offset reaches 1
index = 8  # midway color selection
blend = True  # color blending between palette indices

# initialize list with all pixels off
palette = [0] * num_leds

# Declare a NeoPixel object on led_pin with num_leds as pixels
# No auto-write.
# Set brightness to max.
# We will be using FancyLED's brightness control.
strip = neopixel.NeoPixel(led_pin, num_leds, brightness=1, auto_write=False)

# button setup
button = DigitalInOut(board.D2)
button.direction = Direction.INPUT
button.pull = Pull.UP
prevkeystate = False
ledmode = 0  # button press counter, switch color palettes

# FancyLED allows for assigning a color palette using these formats:
# * The first (5) palettes here are mixing between 2-elements
# * The last (3) palettes use a format identical to the FastLED Arduino Library
# see FastLED - colorpalettes.cpp
forest = [fancy.CRGB(0, 255, 0),  # green
          fancy.CRGB(255, 255, 0)]  # yellow

ocean = [fancy.CRGB(0, 0, 255),  # blue
         fancy.CRGB(0, 255, 0)]  # green

purple = [fancy.CRGB(160, 32, 240),  # purple
          fancy.CRGB(238, 130, 238)]  # violet

all_colors = [fancy.CRGB(0, 0, 0),  # black
              fancy.CRGB(255, 255, 255)]  # white

washed_out = [fancy.CRGB(0, 0, 0),  # black
              fancy.CRGB(255, 0, 255)]  # purple

rainbow = [0xFF0000, 0xD52A00, 0xAB5500, 0xAB7F00,
           0xABAB00, 0x56D500, 0x00FF00, 0x00D52A,
           0x00AB55, 0x0056AA, 0x0000FF, 0x2A00D5,
           0x5500AB, 0x7F0081, 0xAB0055, 0xD5002B]

rainbow_stripe = [0xFF0000, 0x000000, 0xAB5500, 0x000000,
                  0xABAB00, 0x000000, 0x00FF00, 0x000000,
                  0x00AB55, 0x000000, 0x0000FF, 0x000000,
                  0x5500AB, 0x000000, 0xAB0055, 0x000000]

heat_colors = [0x330000, 0x660000, 0x990000, 0xCC0000, 0xFF0000,
               0xFF3300, 0xFF6600, 0xFF9900, 0xFFCC00, 0xFFFF00,
               0xFFFF33, 0xFFFF66, 0xFFFF99, 0xFFFFCC]

def remapRange(value, leftMin, leftMax, rightMin, rightMax):
    # this remaps a value fromhere original (left) range to new (right) range
    # Figure out how 'wide' each range is
    leftSpan = leftMax - leftMin
    rightSpan = rightMax - rightMin

    # Convert the left range into a 0-1 range (int)
    valueScaled = int(value - leftMin) / int(leftSpan)

    # Convert the 0-1 range into a value in the right range.
    return int(rightMin + (valueScaled * rightSpan))

def shortkeypress(color_palette):
    color_palette += 1

    if color_palette > 6:
        color_palette = 1

    return color_palette

while True:

    # check for button press
    currkeystate = button.value

    # button press, move to next pattern
    if (prevkeystate is not True) and currkeystate:
        ledmode = shortkeypress(ledmode)

    # save button press state
    prevkeystate = currkeystate

    # Fire Colors [ HEAT ]
    if ledmode == 1:
        palette = heat_colors

    # Forest
    elif ledmode == 2:
        palette = forest

    # Ocean
    elif ledmode == 3:
        palette = ocean

    # Purple Lovers
    elif ledmode == 4:
        palette = purple

    # All the colors!
    elif ledmode == 5:
        palette = rainbow

    # Rainbow stripes
    elif ledmode == 6:
        palette = rainbow_stripe

    # All the colors except the greens, washed out
    elif ledmode == 7:
        palette = washed_out

    for i in range(num_leds):
        color = fancy.palette_lookup(palette, offset + i / num_leds)
        color = fancy.gamma_adjust(color, brightness=brightness)
        strip[i] = color.pack()

    if fadeup:
        offset += steps
        if offset >= 1:
            fadeup = False
        offset -= steps
        if offset <= 0:
            fadeup = True

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 17, 2014. It was last updated on Dec 17, 2014.

This page (CircuitPython Code) was last updated on Dec 04, 2021.

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