Overview

Wear a bangle of light! Build a charming bracelet from four NeoPixel rings and GEMMA, Adafruit's tiny wearable electronics platform. You will need:

This guide was written for the 'original' Gemma board, but can be done with either the original or M0 Gemma. We recommend the Gemma M0 as it is easier to use and is more compatible with modern computers!

Circuit Diagram

This diagram uses the original Gemma but you can also use the Gemma M0 with the exact same wiring!
Click to enlarge. GEMMA's D1 pin is wired to the first pixel ring's input pin. Signal output of first ring chains to subsequent ring's input pin, and so on.

GEMMA's Vout pin is wired to all four pixel ring's VCC pins. Likewise GEMMA's ground pin is wired to all the rings' GND pins.

Build it!

Lay out four NeoPixel rings on a gridded surface like a cutting mat. Glue on your metal jewelry findings as shown with E6000 craft adhesive and let dry overnight.

The orientation of the rings in the photo above matches up with our coding diagram on the next page. This orientation affects how any multi-ring animations will look!
Open your jump rings by twisting the wire ends away from each other with two pairs of pliers. Torque the wire ends, don't splay them.

Use your jump rings to attach the jewelry findings to one another, and also to attach a magnetic clasp.

Close jump rings the same way you opened them: twist the wire ends towards each other with two pairs of pliers until they match up.
Follow the circuit diagram to connect GEMMA and the four NeoPixel Rings. Use small-gauge stranded wire, and route the wires through the jump rings so they are hidden from the front side of the pixel rings.

Make sure that the wires are not under strain-- they should be long enough to allow the segments of the bracelet to move semi-freely without tugging. The metal findings/jump ring should be responsible for strain relief.
When soldering power and ground connections, where more than one wire will affix to each joint, put both wires in at once before soldering. It's easier to solder two wires at once than it is to solder one wire in, then have to reheat the solder to add another.
You are making a piece of delicate jewelry, but you'll wear it out on your wrist, so there's a chance your wires could get snagged! To provide extra strain relief, add a dot of E6000 over each solder connection on the NeoPixel rings.
To add a power switch, cut and strip one of the wires leading to your battery.

Add two small pieces of heat shrink tubing to the stripped wires and solder to two legs of the small switch (center leg and one outer leg). Slide the heat shrink to cover the exposed metal and shrink with a heat gun.

Use a piece of foam tape to stick the battery behind the GEMMA, with the switch sticking out the side. Plug in the battery and glue the switch in place.

Arduino Code

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!

To program GEMMA, make sure you have set up the Arduino IDE as explained in the "Introducing GEMMA" guide. Also, you’ll need the NeoPixel library installed as explained in the NeoPixel Überguide.

Above is a diagram numbering the NeoPixels in their programatic order. It's handy for writing animations that seem to flow between rings, like the basic sine wave animation here:

//Basic sine wave animation for NeoPixel Ring Bangle Bracelet
//by Dano Wall and Becky Stern for Adafruit Industries
#include <Adafruit_NeoPixel.h>

#define PIN       1 // Marked D1 on GEMMA
#define NUM_LEDS 64

// Parameter 1 = number of pixels in strip
// Parameter 2 = pin number (most are valid)
// Parameter 3 = pixel type:
//   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(NUM_LEDS, PIN, NEO_GRB);

uint32_t color = strip.Color(75, 250, 100); // Change RGB color value here

// These are the pixels in order of animation-- 36 pixels in total:
int sine[] = {
   4,  3,  2,  1,  0, 15, 14, 13, 12, 20, 21, 22, 23, 24, 25, 26, 27, 28,
  36, 35, 34, 33, 32, 47, 46, 45, 44, 52, 53, 54, 55, 56, 57, 58, 59, 60 };

void setup() {
  strip.begin();
  strip.show();            // Initialize all pixels to 'off'
  strip.setBrightness(40); // 40/255 brightness (about 15%)
}

void loop() {
  for(int i=0; i<36; i++) {
    strip.setPixelColor(sine[i], color);             // Draw 'head' pixel
    strip.setPixelColor(sine[(i + 36 - 8) % 36], 0); // Erase 'tail'
    strip.show();
    delay(40);
  }
}
Here's another fun animation, it's similar to the sine wave but loops back around on itself when it gets to the fourth ring in a "figure eight."
//Figure-Eight animation for Neopixel Ring Bangle Bracelet
//By Dano Wall and Becky Stern for Adafruit Industries
#include <Adafruit_NeoPixel.h>

#define PIN       1 // Marked D1 on GEMMA
#define NUM_LEDS 64

// Parameter 1 = number of pixels in strip
// Parameter 2 = pin number (most are valid)
// Parameter 3 = pixel type:
//   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(NUM_LEDS, PIN, NEO_GRB);

uint32_t color = strip.Color(5, 250, 200); // Change RGB color value here

// Array of pixels in order of animation - 70 in total:
int sine[] = {
   4,  3,  2,  1,  0, 15, 14, 13, 12, 20, 21, 22, 23, 24, 25, 26, 27, 28,
  36, 35, 34, 33, 32, 47, 46, 45, 44, 52, 53, 54, 55, 56, 57, 58, 59, 60,
  61, 62, 63, 48, 49, 50, 51, 52, 44, 43, 42, 41, 40, 39, 38, 37, 36, 28,
  29, 30, 31, 16, 17, 18, 19, 20, 12, 11, 10,  9,  8,  7,  6,  5 };

void setup() {
  strip.begin();
  strip.show();            // Initialize all pixels to 'off'
  strip.setBrightness(40); // 40/255 brightness (about 15%)
}

void loop() {
  for(int i=0; i<70; i++) {
    strip.setPixelColor(sine[i], 0);                 // Erase 'tail'
    strip.setPixelColor(sine[(i + 10) % 70], color); // Draw 'head' pixel
    strip.show();
    delay(60);
  }
}
This code randomly flashes pixels in three colors of your choice.
//Random Flash animation for Neopixel Ring Bangle Bracelet
//by Dano Wall and Becky Stern for Adafruit Industries
//based on the Sparkle Skirt, minus the accelerometer
#include <Adafruit_NeoPixel.h>

#define PIN       1 // Marked D1 on GEMMA
#define NUM_LEDS 64

// Parameter 1 = number of pixels in strip
// Parameter 2 = pin number (most are valid)
// Parameter 3 = pixel type:
//   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(NUM_LEDS, PIN, NEO_GRB);

// Here is where you can put in your favorite colors that will appear!
// just add new {nnn, nnn, nnn}, lines. They will be picked out randomly
uint8_t myColors[][3] = {
  {232, 100, 255}, // purple
  {200, 200,  20}, // yellow
  { 30, 200, 200}, // blue
};

// don't edit the line below
#define FAVCOLORS sizeof(myColors) / 3

void setup() {
  strip.begin();
  strip.show();            // Initialize all pixels to 'off'
  strip.setBrightness(40); // 40/255 brightness (about 15%)
}

void loop() {
  flashRandom(5); // Number is 'wait' delay, smaller num = faster twinkle
}

void flashRandom(int wait) {

  // pick a random favorite color!
  int c     = random(FAVCOLORS);
  int red   = myColors[c][0];
  int green = myColors[c][1];
  int blue  = myColors[c][2];

  // get a random pixel from the list
  int j = random(strip.numPixels());

  // now we will fade in over 5 steps
  for (int x=1; x <= 5; x++) {
    int r = red   * x / 5;
    int g = green * x / 5;
    int b = blue  * x / 5;

    strip.setPixelColor(j, strip.Color(r, g, b));
    strip.show();
    delay(wait);
  }
  // & fade out in 5 steps
  for (int x=5; x >= 0; x--) {
    int r = red   * x / 5;
    int g = green * x / 5;
    int b = blue  * x / 5;

    strip.setPixelColor(j, strip.Color(r, g, b));
    strip.show();
    delay(wait);
  }
  // LED will be off when done (they are faded to 0)
}

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 “main.py” 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.

Planning

Above is a diagram numbering the NeoPixels in their programatic order. It's handy for writing animations that seem to flow between rings, like the basic sine wave animation here:

And here’s the CircuitPython code, using a table of pixel numbers to sequence the animation:

import board
import neopixel
import time
try:
	import urandom as random  # for v1.0 API support
except ImportError:
	import random

numpix = 64        # Number of NeoPixels
pixpin = board.D1  # Pin where NeoPixels are connected
strip  = neopixel.NeoPixel(pixpin, numpix, brightness=0.15)
color  = [75, 250, 100]  # RGB color - teal

sine = [ # These are the pixels in order of animation - 36 pixels in total:
   4,  3,  2,  1,  0, 15, 14, 13, 12, 20, 21, 22, 23, 24, 25, 26, 27, 28,
  36, 35, 34, 33, 32, 47, 46, 45, 44, 52, 53, 54, 55, 56, 57, 58, 59, 60 ]

while True:  # Loop forever...
	for i in range(len(sine)):
		# Set 'head' pixel to color:
		strip[sine[i]] = color
		# Erase 'tail,' 8 pixels back:
		strip[sine[(i + len(sine) - 8) % len(sine)]] = [0,0,0]
		strip.write()      # Refresh LED states
		time.sleep(0.016)  # 16 millisecond delay

Here's another fun animation, it's similar to the sine wave but loops back around on itself when it gets to the fourth ring in a "figure eight."

import board
import neopixel
import time
try:
	import urandom as random
except ImportError:
	import random

numpix = 64        # Number of NeoPixels
pixpin = board.D1  # Pin where NeoPixels are connected
strip  = neopixel.NeoPixel(pixpin, numpix, brightness=0.15)
color  = [5, 250, 200]  # RGB color - cyan

sine = [ # These are the pixels in order of animation - 70 pixels in total:
   4,  3,  2,  1,  0, 15, 14, 13, 12, 20, 21, 22, 23, 24, 25, 26, 27, 28,
  36, 35, 34, 33, 32, 47, 46, 45, 44, 52, 53, 54, 55, 56, 57, 58, 59, 60,
  61, 62, 63, 48, 49, 50, 51, 52, 44, 43, 42, 41, 40, 39, 38, 37, 36, 28,
  29, 30, 31, 16, 17, 18, 19, 20, 12, 11, 10,  9,  8,  7,  6,  5 ]

while True:  # Loop forever...
	for i in range(len(sine)):
		# Erase 'tail':
		strip[sine[i]] = [0,0,0]
		# Draw 'head,' 10 pixels ahead:
		strip[sine[(i + 10) % len(sine)]] = color
		strip.write()     # Refresh LED states
		time.sleep(0.04)  # 40 millisecond delay

This code randomly flashes pixels in three colors of your choice.

import board
import neopixel
import time
try:
	import urandom as random
except ImportError:
	import random

numpix = 64        # Number of NeoPixels
pixpin = board.D1  # Pin where NeoPixels are connected
strip  = neopixel.NeoPixel(pixpin, numpix, brightness=0.0)
colors = [
  [ 232, 100, 255 ], # Purple
  [ 200, 200,  20 ], # Yellow
  [  30, 200, 200 ], # Blue
]

while True:  # Loop forever...
	c = random.randint(0, len(colors) - 1)  # Choose random color index
	j = random.randint(0, numpix - 1)       # Choose random pixel
	strip[j] = colors[c]                    # Set pixel to color
	for i in range(1, 5):
		strip.brightness = i / 5.0      # Ramp up brightness
		strip.write()
	for i in range(5, 0, -1):
		strip.brightness = i / 5.0      # Ramp down brightness
		strip.write()
	strip[j] = [0,0,0]                      # Set pixel to 'off'

Wear it!

Enjoy your new bangle bracelet! Perfect a New Year's party, sporting event (with team colors, of course), wedding, bat mitzvah, quinceañera, and more.