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 Gemma M0 and Trinket M0 boards. 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 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.

# Fiery demon horns (rawr!) for Adafruit Trinket/Gemma.
# Adafruit invests time and resources providing this open source code,
# please support Adafruit and open-source hardware by purchasing
# products from Adafruit!

import board
import neopixel
from analogio import AnalogIn
# pylint: disable=global-statement

try:
    import urandom as random
except ImportError:
    import random

# /\  ->   Fire-like effect is the sum_total of multiple triangle
# ____/  \____  waves in motion, with a 'warm' color map applied.
n_horns = 1             # number of horns
led_pin = board.D0      # which pin your pixels are connected to
n_leds = 30             # number of LEDs per horn
frames_per_second = 50  # animation frames per second
brightness = 0          # current wave height
fade = 0                # Decreases brightness as wave moves
pixels = neopixel.NeoPixel(led_pin, n_leds, brightness=1, auto_write=False)
offset = 0

# Coordinate space for waves is 16x the pixel spacing,
# allowing fixed-point math to be used instead of floats.
lower = 0       # lower bound of wave
upper = 1       # upper bound of wave
mid = 2         # midpoint (peak) ((lower+upper)/2)
vlower = 3      # velocity of lower bound
vupper = 4      # velocity of upper bound
intensity = 5   # brightness at peak

y = 0
brightness = 0
count = 0

# initialize 3D list
wave = [[0] * 6] * 6, [[0] * 6] * 6, [[0] * 6] * 6, [[0] * 6] * 6, [[0] * 6] * 6, [[0] * 6] * 6

# Number of simultaneous waves (per horn)
n_waves = len(wave)

# Gamma-correction table
gamma = [
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2,
    2, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 5, 5, 5,
    5, 6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 9, 9, 9, 10,
    10, 10, 11, 11, 11, 12, 12, 13, 13, 13, 14, 14, 15, 15, 16, 16,
    17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 23, 24, 24, 25,
    25, 26, 27, 27, 28, 29, 29, 30, 31, 32, 32, 33, 34, 35, 35, 36,
    37, 38, 39, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 50,
    51, 52, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 66, 67, 68,
    69, 70, 72, 73, 74, 75, 77, 78, 79, 81, 82, 83, 85, 86, 87, 89,
    90, 92, 93, 95, 96, 98, 99, 101, 102, 104, 105, 107, 109, 110,
    112, 114, 115, 117, 119, 120, 122, 124, 126, 127, 129, 131, 133,
    135, 137, 138, 140, 142, 144, 146, 148, 150, 152, 154, 156, 158,
    160, 162, 164, 167, 169, 171, 173, 175, 177, 180, 182, 184, 186,
    189, 191, 193, 196, 198, 200, 203, 205, 208, 210, 213, 215, 218,
    220, 223, 225, 228, 231, 233, 236, 239, 241, 244, 247, 249, 252,
    255
]


def random_wave(he, wi):
    wave[he][wi][upper] = -1                                  # Always start below head of strip
    wave[he][wi][lower] = -16 * (3 + random.randint(0,4))     # Lower end starts ~3-7 pixels back
    wave[he][wi][mid] = (wave[he][wi][lower]+ wave[he][wi][upper]) / 2
    wave[he][wi][vlower] = 3 + random.randint(0,4)            #  Lower end moves at ~1/8 to 1/pixels
    wave[he][wi][vupper] = wave[he][wi][vlower]+ random.randint(0,4) # Upper end moves a bit faster
    wave[he][wi][intensity] = 300 + random.randint(0,600)

def setup():
    global fade

    # 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(board.A0)
    random.seed(pin.value)
    pin.deinit()

    for he in range(n_horns):
        for wi in range(n_waves):
            random_wave(he, wi)

    fade = 233 + n_leds / 2

    if fade > 233:
        fade = 233

setup()

while True:

    h = w = i = r = g = b = 0
    x = 0

    for h in range(n_horns):                # For each horn...
        x = 7
        sum_total = 0
        for i in range(n_leds):             # For each LED along horn...
            x += 16
            for w in range(n_waves):        # For each wave of horn...
                if (x < wave[h][w][lower]) or (x > wave[h][w][upper]):
                    continue                # Out of range
                if x <= wave[h][w][mid]:    # Lower half of wave (ramping up peak brightness)
                    sum_top = wave[h][w][intensity] * (x - wave[h][w][lower])
                    sum_bottom = (wave[h][w][mid] - wave[h][w][lower])
                    sum_total += sum_top /  sum_bottom
                else:                       # Upper half of wave (ramping down from peak)
                    sum_top = wave[h][w][intensity] * (wave[h][w][upper] - x)
                    sum_bottom = (wave[h][w][upper] - wave[h][w][mid])
                    sum_total += sum_top / sum_bottom

            sum_total = int(sum_total)          # convert from decimal to whole number

            # Now the magnitude (sum_total) is remapped to color for the LEDs.
            # A blackbody palette is used - fades white-yellow-red-black.
            if sum_total < 255:                 # 0-254 = black to red-1
                r = gamma[sum_total]
                g = b = 0
            elif sum_total < 510:               # 255-509 = red to yellow-1
                r = 255
                g = gamma[sum_total - 255]
                b = 0
            elif sum_total < 765:               # 510-764 = yellow to white-1
                r = g = 255
                b = gamma[sum_total - 510]
            else:                               # 765+ = white
                r = g = b = 255
            pixels[i] = (r, g, b)

    for w in range(n_waves):                    # Update wave positions for each horn
        wave[h][w][lower] += wave[h][w][vlower] # Advance lower position
        if wave[h][w][lower] >= (n_leds * 16):  # Off end of strip?
            random_wave(h, w)                   # Yes, 'reboot' wave
        else:                                   # No, adjust other values...
            wave[h][w][upper] += wave[h][w][vupper]
            wave[h][w][mid] = (wave[h][w][lower] + wave[h][w][upper]) / 2
            wave[h][w][intensity] = (wave[h][w][intensity] * fade) / 256 # Dimmer

    pixels.show()

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.

This guide was first published on May 28, 2014. It was last updated on May 28, 2014.

This page (CircuitPython Code) was last updated on Jun 13, 2021.

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