GEMMA M0 and Trinket M0 boards can run CircuitPython — a different approach to programming compared to Arduino sketches. In fact, CircuitPython comes factory pre-loaded on GEMMA M0 and Trinket 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 and the Adafruit Trinket M0 guide.

These directions are specific to the “M0” boards. The original GEMMA and Trinket 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 or Trinket 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 or Trinket M0 doesn’t show up as a drive, follow the GEMMA M0 or Trinket M0 guide link above to prepare the board for CircuitPython.

You’ll need to change one line #6 which represents the output pin that controls the NeoPixels.

If using Trinket M0:

pixpin = board.D4

If using GEMMA M0:

pixpin = board.D1
# SPDX-FileCopyrightText: 2017 Mikey Sklar for Adafruit Industries
# SPDX-License-Identifier: MIT

import time

import board
import neopixel

numpix = 22  # Number of NeoPixels
pixpin = board.D1  # NeoPixels pin. For Gemma M0 = D1, Trinket M0 = D4
strip = neopixel.NeoPixel(pixpin, numpix, brightness=1, auto_write=False)
pos = 0  # position
direction = 1  # direction of "eye"

while True:
    strip[pos - 2] = ([16, 0, 0])  # Dark red
    strip[pos - 1] = ([128, 0, 0])  # Medium red
    strip[pos] = ([255, 48, 0])  # brightest
    strip[pos + 1] = ([128, 0, 0])  # Medium red

    if (pos + 2) < numpix:
        # Dark red, do not exceed number of pixels
        strip[pos + 2] = ([16, 0, 0])


    # Rather than being sneaky and erasing just the tail pixel,
    # it's easier to erase it all and draw a new one next time.
    for j in range(-2, 2):
        strip[pos + j] = (0, 0, 0)
        if (pos + 2) < numpix:
            strip[pos + 2] = (0, 0, 0)

    # Bounce off ends of strip
    pos += direction
    if pos < 0:
        pos = 1
        direction = -direction
    elif pos >= (numpix - 1):
        pos = numpix - 2
        direction = -direction

This code can also work on an Adafruit Hallowing board with just a small change to lines 6 and 7:

numpix = 30
pixpin = board.EXTERNAL_NEOPIXEL

This guide was first published on Sep 23, 2013. It was last updated on Jun 23, 2024.

This page (CircuitPython Code) was last updated on Jun 23, 2024.

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