The Arduino code presented below works equally well on all versions of GEMMA: v1, v2 and M0. But if you have an M0 board, consider using the CircuitPython code on the next page of this guide, no Arduino IDE required!
If this is your first time using GEMMA, work through the Introducing GEMMA guide first; you need to customize some settings in the Arduino IDE. Once you have it up and running (test the 'blink' sketch), then follow the instructions on the following page for installing the NeoPixel library:
Plug in your circuit and load up the sketch below:
// SPDX-FileCopyrightText: 2017 Phillip Burgess for Adafruit Industries
//
// SPDX-License-Identifier: MIT
// Low power NeoPixel earrings example. Makes a nice blinky display
// with just a few LEDs on at any time...uses MUCH less juice than
// rainbow display!
#include <Adafruit_NeoPixel.h>
#define PIN 0
#define NUM_LEDS 16
Adafruit_NeoPixel pixels = Adafruit_NeoPixel(NUM_LEDS, PIN);
uint8_t mode = 0, // Current animation effect
offset = 0; // Position of spinner animation
uint32_t color = 0xFF8000; // Starting color = amber
uint32_t prevTime; // Time of last animation mode switch
void setup() {
pixels.begin();
pixels.setBrightness(60); // ~1/3 brightness
prevTime = millis(); // Starting time
}
void loop() {
uint8_t i;
uint32_t t;
switch(mode) {
case 0: // Random sparkles - just one LED on at a time!
i = random(NUM_LEDS); // Choose a random pixel
pixels.setPixelColor(i, color); // Set it to current color
pixels.show(); // Refresh LED states
// Set same pixel to "off" color now but DON'T refresh...
// it stays on for now...both this and the next random
// pixel will be refreshed on the next pass.
pixels.setPixelColor(i, 0);
delay(10); // 10 millisecond delay
break;
case 1: // Spinny wheel (4 LEDs on at a time)
for(i=0; i<NUM_LEDS; i++) { // For each LED...
uint32_t c = 0; // Assume pixel will be "off" color
if(((offset + i) & 7) < 2) { // For each 8 pixels, 2 will be...
c = color; // ...assigned the current color
}
pixels.setPixelColor(i, c); // Set color of pixel 'i'
}
pixels.show(); // Refresh LED states
delay(50); // 50 millisecond delay
offset++; // Shift animation by 1 pixel on next frame
break;
// More animation modes could be added here!
}
t = millis(); // Current time in milliseconds
if((t - prevTime) > 8000) { // Every 8 seconds...
mode++; // Advance to next animation mode
if(mode > 1) { // End of modes?
mode = 0; // Start over from beginning
color >>= 8; // And change color
if(!color) color = 0xFF8000; // preiodically reset to amber
}
pixels.clear(); // Set all pixels to 'off' state
prevTime = t; // Record the time of the last mode change
}
}
Page last edited December 01, 2025
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