CircuitPython Code

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 “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.

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.

This guide was first published on Nov 04, 2015. It was last updated on Nov 04, 2015. This page (CircuitPython Code) was last updated on May 30, 2020.