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 “” 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

pixpin = board.D1
numpix = 7
wait = .5  # 1/2 second color fade duration

# defaults to RGB|GRB Neopixels
strip = neopixel.NeoPixel(pixpin, numpix, brightness=1, auto_write=False)

# uncomment the following 3 line for RGBW Neopixels
# strip = neopixel.NeoPixel(
# pixpin, numpix, bpp=4, brightness=.3, auto_write=True
# )

# Linear interpolation of y value given min/max x, min/max y, and x position.

def lerp(x, x0, x1, y0, y1):
    # Clamp x within x0 and x1 bounds.
    if x > x1:
        x = x1

    if x < x0:
        x = x0

    # Calculate linear interpolation of y value.
    return y0 + (y1 - y0) * ((x - x0) / (x1 - x0))

# Set all pixels to the specified color.

def fill_pixels(r, g, b):
    for i in range(0, numpix):
        strip[i] = (r, g, b)

# Get the color of a pixel within a smooth gradient of two colors.
# Starting R,G,B color
# Ending R,G,B color
# Position along gradient, should be a value 0 to 1.0

def color_gradient(start_r, start_g, start_b, end_r, end_g, end_b, pos):
    # Interpolate R,G,B values and return them as a color.
    red = lerp(pos, 0.0, 1.0, start_r, end_r)
    green = lerp(pos, 0.0, 1.0, start_g, end_g)
    blue = lerp(pos, 0.0, 1.0, start_b, end_b)

    return (red, green, blue)

# Starting R,G,B color
# Ending R,G,B color
# Total duration of animation, in milliseconds

def animate_gradient_fill(start_r, start_g, start_b, end_r, end_g, end_b,
    start = time.monotonic()

    # Display start color.
    fill_pixels(start_r, start_g, start_b)

    # Main animation loop.
    delta = time.monotonic() - start

    while delta < duration_ms:
        # Calculate how far along we are in the duration as a position 0...1.0
        pos = delta / duration_ms
        # Get the gradient color and fill all the pixels with it.
        color = color_gradient(start_r, start_g, start_b,
                               end_r, end_g, end_b, pos)
        fill_pixels(int(color[0]), int(color[1]), int(color[2]))
        # Update delta and repeat.
        delta = time.monotonic() - start

    # Display end color.
    fill_pixels(end_r, end_g, end_b)

while True:
    # Run It:

    # Nice fade from dim red to full red for 1/2 of a second:
    animate_gradient_fill(10, 0, 0, 255, 0, 0, wait)

    # Then fade from full red to dim red for 1/2 a second.
    animate_gradient_fill(255, 0, 0, 10, 0, 0, wait)

    # time.sleep(1) # Use this delay if using multiple color fades

This code requires the 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 from Github.

This guide was first published on Apr 05, 2017. It was last updated on Apr 05, 2017. This page (CircuitPython Code) was last updated on May 22, 2019.