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!

Software Setup

If this is your first time using Arduino and Gemma, take a look at Adafruit Gemma M0 or Introducing Gemma to get a guided tour.  You'll also want to be sure the Adafruit_NeoPixel library is installed in Arduino:

(Sketch > Include Library > Manage Libraries...)

In the demo video, we're using the Strandtest code that comes with the Neopixel library.  Strandtest is great to start with, but it's a little bit "loud" for a necklace.  

Here is some slightly quieter code that displays a gorgeous rainbow effect with three different modes for variations in speed and interest.

Go to your Tools menu and select Gemma from the list of boards.  Plug your Gemma into your computer via the onboard USB port.  Press the "reset" button on your Gemma and wait for the blinky red light, then click the upload button in Arduino.

#include <Adafruit_NeoPixel.h>

#define PIN 1

Adafruit_NeoPixel pixels = Adafruit_NeoPixel(40, PIN);

uint8_t  mode   = 0, // Current animation effect
         offset = 0;
uint32_t color  = 0X00A4B3; // Starting color
uint32_t prevTime; 

void setup() {
  pixels.begin();
  pixels.setBrightness(40); // 1/3 brightness
  prevTime = millis();
}

void loop() {
  uint8_t  i;
  uint32_t t;

  switch(mode) {
    
   case 0: //rainbow hold
    rainbowHold(20);
    delay(500);
    break;
    
   case 1: //rainbow cycle slow
    rainbowCycleslow(20);
    delay(50);
    break;
       
   case 2: //rainbow cycle fast 
    rainbowCycle(5);
    delay(50);
    break;
  }

  t = millis();
  if((t - prevTime) > 8000) {      // Every 8 seconds...
    mode++;                        // Next mode
    if(mode > 3) {                 // End of modes?
      mode = 0;                    // Start modes over
      color >>= 8;                 // Next color R->G->B
      if(!color) color = 0xB300A4; // Reset color
    }
    for(i=0; i<32; i++) pixels.setPixelColor(i, 0);
    prevTime = t;
    
  }

  
}
void rainbow(uint8_t wait) {
  uint16_t i, j;

  for(j=0; j<256; j++) {
    for(i=0; i<pixels.numPixels(); i++) {
      pixels.setPixelColor(i, Wheel((i+j) & 255));
    }
    pixels.show();
    delay(wait);
  }
}

void rainbowCycle(uint8_t wait) {
  uint16_t r, j;

  for(j=0; j<256*6; j++) { // 6 cycles of all colors on wheel
    for(r=0; r< pixels.numPixels(); r++) {
      pixels.setPixelColor(r, Wheel(((r * 256 / pixels.numPixels()) + j) & 255));
    }
    pixels.show();
    delay(wait);
  }
}
void rainbowCycleslow(uint8_t wait) {
  uint16_t r, j;

  for(j=0; j<256*3; j++) { // 3 cycles of all colors on wheel
    for(r=0; r< pixels.numPixels(); r++) {
      pixels.setPixelColor(r, Wheel(((r * 256 / pixels.numPixels()) + j) & 255));
    }
    pixels.show();
    delay(wait);
  }
}
void rainbowHold(uint8_t wait) {
  uint16_t r, j;

  for(j=0; j<256*1; j++) { // 3 cycles of all colors on wheel
    for(r=0; r< pixels.numPixels(); r++) {
      pixels.setPixelColor(r, Wheel(((r * 256 / pixels.numPixels()) + j) & 255));
    }
    pixels.show();
    delay(wait);
  }
}

// Input a value 0 to 255 to get a color value.
// The colours are a transition r - g - b - back to r.
uint32_t Wheel(byte WheelPos) {
  if(WheelPos < 85) {
   return pixels.Color(WheelPos * 3, 255 - WheelPos * 3, 0);
  } else if(WheelPos < 170) {
   WheelPos -= 85;
   return pixels.Color(255 - WheelPos * 3, 0, WheelPos * 3);
  } else {
   WheelPos -= 170;
   return pixels.Color(0, WheelPos * 3, 255 - WheelPos * 3);
  }
}

Taking a look at the code, you'll see that there are a few

variables at the top you can change.

Adafruit_NeoPixel pixels = Adafruit_NeoPixel(40, PIN);

Change this number to make the rainbow appear more or less spread out.  We really only have 7 pixels, but to slow the animation down I've told the Gemma we have 40.

 pixels.setBrightness(40);

Set the brightness here.  Max is 255, but that will blind people.  40 is just bright enough that people will notice both you AND your necklace.

rainbowHold(20);
delay(500);

Play with these numbers to speed up or slow down the animation, or to keep one animation running longer.

 

If you encounter trouble…

Any time you hit a roadblock with a neopixel project, we’ll usually ask that you start with the “strandtest” example from our own Adafruit_NeoPixel library. 

You’ll find the strandtest example under File→Sketchbook→Libraries→Adafruit_NeoPixel→strandtest

If strandtest fails to run, this suggests a hardware issue…for example, connecting to the wrong Gemma pin.  Make sure you've wired your neopixels to pin 1, and that they're wired to the "in" rather than the "out" pin on the Jewel.

Last updated on Dec 12, 2017 Published on May 17, 2017