Arduino Code

Plug your GEMMA into your computer with a USB cable. Make sure you've followed the Introducing GEMMA guide and have the NeoPixel library installed. Load the following sketch onto GEMMA with the Arduino IDE:

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!
#include <Adafruit_NeoPixel.h>

#define PIN 1

// Parameter 1 = number of pixels in strip
// Parameter 2 = pin number (most are valid)
// Parameter 3 = pixel type flags, add together as needed:
//   NEO_KHZ800  800 KHz bitstream (most NeoPixel products w/WS2812 LEDs)
//   NEO_KHZ400  400 KHz (classic 'v1' (not v2) FLORA pixels, WS2811 drivers)
//   NEO_GRB     Pixels are wired for GRB bitstream (most NeoPixel products)
//   NEO_RGB     Pixels are wired for RGB bitstream (v1 FLORA pixels, not v2)
Adafruit_NeoPixel strip = Adafruit_NeoPixel(5, PIN, NEO_GRB + NEO_KHZ800);

void setup() {
  strip.begin();; // Initialize all pixels to 'off'

void loop() {
  // all pixels show the same color:
  colorWipe(strip.Color(50, 0, 50), 50); // Purple

// Fill the dots one after the other with a color
void colorWipe(uint32_t c, uint8_t wait) {
  for(uint16_t i=0; i<strip.numPixels(); i++) {
      strip.setPixelColor(i, c);;

Installing Arduino libraries is a frequent stumbling block. If this is your first time, or simply needing a refresher, please read the All About Arduino Libraries tutorial.If the library is correctly installed (and the Arduino IDE is restarted), you should be able to navigate through the “File” rollover menus as follows:


Connect up your NeoPixels in a solderless breadboard and use alligator clips to attach to GEMMA, referring to the circuit diagram if necessary.

You’ll need to change a few lines in the code regarding the data pin (1), type of pixels (RGB vs GRB), and number of pixels (5). The resulting (and slightly simplified) code is below:

From the Tools→Board menu, select the device you are using: 

  • Adafruit Gemma M0
  • Adafruit Gemma 8 MHz 
  • Connect the USB cable between the computer and your device. The original Gemma (8 MHz) need the reset button pressed on the board, then click the upload button (right arrow icon) in the Arduino IDE. You do not need to press the reset on the newer Gemma M0 or Trinket M0.

Disconnect the USB cable and load your battery pack with two CR2032 batteries. Flip on the power switch to test your pixels! If they're not all on or anything's getting hot, turn the power off and inspect your circuit with a multimeter for shorts or poor connections.

Last updated on 2017-10-08 at 03.06.30 PM Published on 2013-10-09 at 01.22.25 PM