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.
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 “main.py” 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 Mikey Sklar for Adafruit Industries # # SPDX-License-Identifier: MIT import time import board import neopixel from analogio import AnalogIn try: import urandom as random except ImportError: import random wick_pin = board.D0 # The data-in pin of the NeoPixel unconnected_pin = board.A0 # Any unconnected pin, to generate random seed # The LED can be in only one of these states at any given time bright = 0 up = 1 down = 2 dim = 3 bright_hold = 4 dim_hold = 5 # Percent chance the LED will suddenly fall to minimum brightness index_bottom_percent = 10 # Absolute minimum red value (green value is a function of red's value) index_bottom = 128 # Minimum red value during "normal" flickering (not a dramatic change) index_min = 192 index_max = 255 # Maximum red value # Decreasing brightness will take place over a number of milliseconds down_min_msecs = 20 down_max_msecs = 250 # Increasing brightness will take place over a number of milliseconds up_min_msecs = 20 up_max_msecs = 250 # Percent chance the color will hold unchanged after brightening bright_hold_percent = 20 # When holding after brightening, hold for a number of milliseconds bright_hold_min_msecs = 0 bright_hold_max_msecs = 100 # Percent chance the color will hold unchanged after dimming dim_hold_percent = 5 # When holding after dimming, hold for a number of milliseconds dim_hold_min_msecs = 0 dim_hold_max_msecs = 50 numpix = 1 # Number of NeoPixels pixpin = board.D0 # Pin where NeoPixels are connected strip = neopixel.NeoPixel(pixpin, numpix, brightness=1, auto_write=True) # initialize strip # Random number generator is seeded from an unused 'floating' # analog input - this helps ensure the random color choices # aren't always the same order. pin = AnalogIn(unconnected_pin) random.seed(pin.value) pin.deinit() index_start = 255 index_start = 255 index_end = 255 state = bright def set_color(index): index = max(min(index, index_max), index_bottom) if index >= index_min: strip[0] = [index, int((index * 3) / 8), 0] elif index < index_min: strip[0] = [index, int((index * 3.25) / 8), 0] set_color(255) while True: current_time = time.monotonic() # BRIGHT if state == bright: flicker_msecs = random.randint( 0, down_max_msecs - down_min_msecs) + down_min_msecs flicker_start = current_time index_start = index_end is_index_in_range = index_start > index_bottom is_random_in_range = random.randint(0, 100) < index_bottom_percent if is_index_in_range and is_random_in_range: index_end = random.randint( 0, index_start - index_bottom) + index_bottom else: index_end = random.randint(0, index_start - index_min) + index_min state = down # DIM elif state == dim: flicker_msecs = random.randint( 0, up_max_msecs - up_min_msecs) + up_min_msecs flicker_start = current_time index_start = index_end index_end = random.randint(0, (index_max - index_start)) + index_min state = down # DIM_HOLD elif state == dim_hold: # dividing flicker_msecs by 1000 to convert to milliseconds if current_time >= (flicker_start + (flicker_msecs / 1000)): if state == bright_hold: state = bright else: state = dim # DOWN elif state == down: # dividing flicker_msecs by 1000 to convert to milliseconds if current_time < (flicker_start + (flicker_msecs / 1000)): index_range = index_end - index_start time_range = (current_time - flicker_start) * 1.0 set_color(index_start + int( (index_range * (time_range / flicker_msecs)))) else: set_color(index_end) if state == down: if random.randint(0, 100) < dim_hold_percent: flicker_start = current_time dim_max = dim_hold_max_msecs - dim_hold_min_msecs flicker_msecs = random.randint( 0, dim_max ) + dim_hold_min_msecs state = dim_hold else: state = dim else: if random.randint(0, 100) < bright_hold_percent: flicker_start = current_time max_flicker = bright_hold_max_msecs - bright_hold_min_msecs flicker_msecs = random.randint( 0, max_flicker) + bright_hold_min_msecs state = bright_hold else: state = bright
This code requires the neopixel.py 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 neopixel.py from Github.
Page last edited January 22, 2025
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