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

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

# SPDX-FileCopyrightText: 2018 Mikey Sklar for Adafruit Industries
# SPDX-License-Identifier: MIT

# 'Cyber falls' sketch
# Creates a fiery rain-like effect on multiple NeoPixel strips.
# Requires Adafruit Trinket and NeoPixel strips.  Strip length is
# inherently limited by Trinket RAM and processing power; this is
# written for five 15-pixel strands, which are paired up per pin
# for ten 15-pixel strips total.

import time
import board
import neopixel
import adafruit_fancyled.adafruit_fancyled as fancy

num_leds = 15       # number of LEDs per strip
saturation = 255    # 0-255, 0 is pure white, 255 is fully saturated color
blend = True        # color blending between palette indices
brightness = 0.5    # half brightness the range is 0.0 - 1.0
concurrent = 3      # number of LEDs on at a time
on_time = 0.04      # 0.04 seconds == 40 milliseconds

# NeoPixel objects using all five Trinket M0 GPIO pins 0-4
drop0 = neopixel.NeoPixel(board.D0, num_leds)
drop1 = neopixel.NeoPixel(board.D1, num_leds)
drop2 = neopixel.NeoPixel(board.D2, num_leds)
drop3 = neopixel.NeoPixel(board.D3, num_leds)
drop4 = neopixel.NeoPixel(board.D4, num_leds)

# list of neopixel strips
drop_list = [drop0, drop1, drop2, drop3, drop4]

def led_drops(strip):

    # FancyLED allows for mixing colors with palettes
    palette = [fancy.CRGB(200, 255, 200),       # lighter (more white) green
               fancy.CRGB(0, 255, 0)]           # full green

    for i in range(num_leds):
        # FancyLED can handle the gamma adjustment, brightness and RGB settings
        color = fancy.palette_lookup(palette, i / num_leds)
        color = fancy.gamma_adjust(color, brightness=brightness)
        strip[i] = color.pack()

        # turn off the LEDs as we go for raindrop effect
        if  i >= concurrent:
            strip[i - concurrent] = (0,0,0)

        if i >= num_leds - 1:
            for j in range(concurrent,-1,-1):
                strip[i-j] = (0,0,0)


while True:

    # loop through each neopixel strip in our list
    for drops in drop_list:

Installing Libraries:

This code requires two libraries be installed:

  • neopixel
  • adafruit_fancyled

 A factory-fresh board will have the neopixel library already installed. If you’ve just reloaded the board with CircuitPython, create the “lib” directory and then copy in the neopixel.mpy and adafruit_fancyled folder from the latest release of the Adafruit_CircuitPython_Bundle

The FancyLED library being using in this CircuitPython example is not the same as the FastLEDused for Arduino. FancyLED has a subset of FastLED features and some different syntax. The FancyLED tutorial provides an excellent overview

The file system layout on your gemma M0 should look like this:

$ pwd
$ find .

This guide was first published on Oct 30, 2013. It was last updated on Jul 16, 2024.

This page (CircuitPython Code) was last updated on Jul 16, 2024.

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