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).

This project is designed to work with RGB NeoPixel rings, not RGBW. The code will not work with RGBW.

If GEMMA M0 doesn’t show up as a drive, follow the GEMMA M0 guide link above to prepare the board for CircuitPython.

# NeoPixel earrings example.  Makes a nice blinky display with just a
# few LEDs on at any time...uses MUCH less juice than rainbow display!

import time

import board
import neopixel
import adafruit_dotstar

try:
    import urandom as random  # for v1.0 API support
except ImportError:
    import random

dot = adafruit_dotstar.DotStar(board.APA102_SCK, board.APA102_MOSI, 1, brightness=0.2)
dot[0] = (0, 0, 0)

numpix = 16  # Number of NeoPixels (e.g. 16-pixel ring)
pixpin = board.D0  # Pin where NeoPixels are connected
strip = neopixel.NeoPixel(pixpin, numpix, brightness=.3, auto_write=False)


def wheel(pos):
    # Input a value 0 to 255 to get a color value.
    # The colours are a transition r - g - b - back to r.
    if pos < 0 or pos > 255:
        return (0, 0, 0)
    if pos < 85:
        return (int(255 - pos*3), int(pos*3), 0)
    if pos < 170:
        pos -= 85
        return (0, int(255 - pos*3), int(pos*3))
    pos -= 170
    return (int(pos * 3), 0, int(255 - (pos*3)))


mode = 0  # Current animation effect
offset = 0  # Position of spinner animation
hue = 0  # Starting hue
color = wheel(hue & 255)  # hue -> RGB color
prevtime = time.monotonic()  # Time of last animation mode switch

while True:  # Loop forever...
    if mode == 0:  # Random sparkles - lights just one LED at a time
        i = random.randint(0, numpix - 1)  # Choose random pixel
        strip[i] = color   # Set it to current color
        strip.show()       # Refresh LED states
        # Set same pixel to "off" color now but DON'T refresh...
        # it stays on for now...bot this and the next random
        # pixel will be refreshed on the next pass.
        strip[i] = [0, 0, 0]
        time.sleep(0.008)  # 8 millisecond delay
    elif mode == 1:  # Spinny wheel (4 LEDs on at a time)
        for i in range(numpix):  # For each LED...
            if ((offset + i) & 7) < 2:  # 2 pixels out of 8...
                strip[i] = color    # are set to current color
            else:
                strip[i] = [0, 0, 0]  # other pixels are off
        strip.show()     # Refresh LED states
        time.sleep(0.04) # 40 millisecond delay
        offset += 1      # Shift animation by 1 pixel on next frame
        if offset >= 8:
            offset = 0
    # Additional animation modes could be added here!

    t = time.monotonic()  # Current time in seconds
    if (t - prevtime) >= 8:  # Every 8 seconds...
        mode += 1  # Advance to next mode
        if mode > 1:  # End of modes?
            mode = 0  # Start over from beginning
            hue += 80  # And change color
            color = wheel(hue & 255)
        strip.fill([0, 0, 0])  # Turn off all pixels
        prevtime = t  # Record time of last mode change

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 Sep 18, 2013. It was last updated on Sep 18, 2013. This page (CircuitPython Code) was last updated on Jun 21, 2019.