Arduino Library

Author Gravatar Image PHILLIP BURGESS
Controlling NeoPixels “from scratch” is quite a challenge, so we provide a library letting you focus on the fun and interesting bits. The library works with most mainstream Arduino boards and derivatives: Uno, Mega, Leonardo, Micro, Adafruit Flora, etc. — most anything with an Atmel AVR 8-bit processor from 8 to 16 MHz — and also works with the Arduino Due and all varieties of the PJRC Teensy boards.

Because processor-specific assembly language is used, this library does not work on Netduino, ChipKIT or other advanced “Arduino-like” boards. Others may have written code and libraries for such boards, but we can’t provide technical support for any bugs or trouble there; that’s frontier stuff. Some of this is covered in the “Advanced Coding” section.
Installation of the library is as follows:
  1. Visit the Adafruit_NeoPixel library page at Github.com.
  2. Select the “Download ZIP” button, or simply click this link to download directly.
  3. Uncompress the ZIP file after it’s finished downloading.
  4. The resulting folder should contain the files “Adafruit_NeoPixel.cpp”, “Adafruit_NeoPixel.h” and an “examples” sub-folder. Sometimes in Windows you’ll get an intermediate-level folder and need to move things around.
  5. Rename the folder (containing the .cpp and .h files) to “Adafruit_NeoPixel” (with the underscore and everything), and place it alongside your other Arduino libraries, typically in your (home folder)/Documents/Arduino/Libraries folder. Libraries should not be installed alongside the Arduino application itself.
  6. Re-start the Arduino IDE if it’s currently running.
Here’s a tutorial that walks through the process of correctly installing Arduino libraries.

Basic Connections

To get started, let’s assume you have some model of Arduino microcontroller connected to the computer’s USB port. We’ll elaborate on the finer points of powering NeoPixels later, but for now you should use a separate 5V DC power supply (or a 3.7V lithium-ion battery for a Flora wearable project).

Identify the “input” end of your NeoPixel strip, pixel(s) or other device. On some, there will be a solder pad labeled “DIN” or “DI” (data input). Others will have an arrow showing the direction that data moves. The data input can originate from any digital pin on the Arduino, but all the example code is set up for digital pin 6 by default. The NeoPixel shield comes wired this way.

If using Flora with an attached lithium-ion battery: connect the +5V input on the strip to the VBATT pad on Flora, GND from the strip to any GND pad on Flora, and DIN to Flora pin D6.

For other Arduino boards with a separate +5V DC power supply for the NeoPixels: connect the +5V input on the strip to the + (positive) terminal on the power supply (don’t connect to the Arduino), DIN to digital pin 6 on the Arduino, and – (minus or GND) on the strip must connect to both the minus (–) terminal on the DC supply and a GND pin on the Arduino (there are usually several — any will do).

The 144 pixel strips are so tightly packed, there’s no room for labels other than –, + and the data direction arrows. Data is the un-labeled pad.
The order of the three pins can vary between different strip densities and batches. ALWAYS use the labels printed ON THE STRIP. Look closely, NEVER blindly follow a NeoPixel strip wiring diagram; it might be based on a different strip type!
When connecting NeoPixels to any live power source or microcontroller, ALWAYS CONNECT GROUND (–) BEFORE ANYTHING ELSE. Conversely, disconnect ground last when separating.
Adding a ~470 ohm resistor between your microcontroller's data pin and the data input on the NeoPixels can help prevent spikes on the data line that can damage your first pixel. Please add one between your micro and NeoPixels!
We also recommend adding a large capacitor (1000 µF, 6.3V or higher) across the + and – terminals. This prevents the initial onrush of current from damaging the pixels. See the photo on the next page for an example.

Can NeoPixels be powered directly from the Arduino’s 5V pin?

Sometimes. The Arduino can continuously supply only about 500 milliamps to the 5V pin. Each NeoPixel can draw up to 60 milliamps at full brightness. So yes, you can skip the separate DC supply and power directly off the Arduino as long as just a few pixels are used, or more if the colors and overall brightness are low. When in doubt, give the pixels a separate power supply.

A Simple Code Example: strandtest

Launch the Arduino IDE. From the File menu, select SketchbookLibrariesAdafruit_NeoPixelstrandtest

(If the Adafruit_NeoPixel rollover menu is not present, the library has not been correctly installed, or the IDE needs to be restarted after installation. Check the installation steps above to confirm it’s properly named and located.)

Select your board type and serial port from the Tools menu, and try uploading to the board. If the NeoPixels are connected and powered, you should see a little light show.

Nothing happens!

Check your connections. The most common mistake is connecting to the output end of a strip rather than the input.
Let’s look at the code now…

All NeoPixel sketches begin by including the header file:
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#include <Adafruit_NeoPixel.h>
The block of code that follows is mostly descriptive comments. Only the last line is really doing any work:
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      #define PIN 6

// 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(60, PIN, NEO_GRB + NEO_KHZ800);
    
The first line assigns a number to the symbol “PIN” for later reference. It doesn’t need to be done this way, but makes it easier to change the pin where the NeoPixels are connected without digging deeper into the code.

The last line declares a NeoPixel object. We’ll refer to this by name later to control the strip of pixels. There are three parameters or arguments in parenthesis:
  1. The number of sequential NeoPixels in the strip. In the example this is set to 60, equal to 1 meter of medium-density strip. Change this to match the actual number you’re using.
  2. The pin number to which the NeoPixel strip (or other device) is connected. Normally this would be a number, but we previously declared the symbol PIN to refer to it by name here.
  3. A value indicating the type of NeoPixels that are connected. In most cases you can leave this off and pass just two arguments; the example code is just being extra descriptive. If you have a supply of classic “V1” Flora pixels, those require NEO_KHZ400 + NEO_RGB to be passed here.
For through-hole 8mm NeoPixels, use NEO_RGB instead of NEO_GRB in the strip declaration.
Then, in the setup() function, call begin() to prepare the data pin for NeoPixel output:
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void setup() {
  strip.begin();
  strip.show(); // Initialize all pixels to 'off'
}
The second line, strip.show(), isn’t absolutely necessary, it’s just there to be thorough. That function pushes data out to the pixels…since no colors have been set yet, this initializes all the NeoPixels to an initial “off” state in case some were left lit by a prior program.
In the strandtest example, loop() doesn’t set any pixel colors on its own — it calls other functions that create animated effects. So let’s ignore it for now and look ahead, inside the individual functions, to see how the strip is controlled.

There are two ways to set the color of a pixel. The first is:
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strip.setPixelColor(n, red, green, blue);
The first argument — n in this example — is the pixel number along the strip, starting from 0 closest to the Arduino. If you have a strip of 30 pixels, they’re numbered 0 through 29. It’s a computer thing. You’ll see various places in the code using a for loop, passing the loop counter variable as the pixel number to this function, to set the values of multiple pixels.

The next three arguments are the pixel color, expressed as red, green and blue brightness levels, where 0 is dimmest (off) and 255 is maximum brightness.

To set the 12th pixel (#11, counting from 0) to magenta (red + blue), you could write:
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strip.setPixelColor(11, 255, 0, 255);
An alternate syntax has just two arguments:
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strip.setPixelColor(n, color);
Here, color is a 32-bit type that merges the red, green and blue values into a single number. This is sometimes easier or faster for some (but not all) programs to work with; you’ll see the strandtest code uses both syntaxes in different places.

You can also convert separate red, green and blue values into a single 32-bit type for later use:
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uint32_t magenta = strip.Color(255, 0, 255);
Then later you can just pass “magenta” as an argument to setPixelColor rather than the separate red, green and blue numbers every time.
setPixelColor() does not have an immediate effect on the LEDs. To “push” the color data to the strip, call show():
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strip.show();
This updates the whole strip at once, and despite the extra step is actually a good thing. If every call to setPixelColor() had an immediate effect, animation would appear jumpy rather than buttery smooth.
You can query the color of a previously-set pixel using getPixelColor():
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uint32_t color = strip.getPixelColor(11);
This returns a 32-bit merged color value.
The number of pixels in a previously-declared strip can be queried using numPixels():
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uint16_t n = strip.numPixels();
The overall brightness of all the LEDs can be adjusted using setBrightness(). This takes a single argument, a number in the range 0 (off) to 255 (max brightness). For example, to set a strip to 1/4 brightness:
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strip.setBrightness(64);
Just like setPixel(), this does not have an immediate effect. You need to follow this with a call to show().

You can’t move from a lower brightness to a higher setting without some loss in fidelity. Certain animation effects are better served by leaving the brightness at max and calling setPixel() repeatedly to fill the strip.

I’m calling setPixel() but nothing’s happening!

There are two main culprits for this:
  1. forgetting to call strip.begin() in setup().
  2. forgetting to call strip.show() after setting pixel colors.
Another (less common) possibility is running out of RAM — see the last section below. If the program sort of works but has unpredictable results, consider that.

Can I have multiple NeoPixel objects on different pins?

Certainly! Each requires its own declaration with a unique name:
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Adafruit_NeoPixel strip_a = Adafruit_NeoPixel(16, 5);
Adafruit_NeoPixel strip_b = Adafruit_NeoPixel(16, 6);
The above declares two distinct NeoPixel objects, one each on pins 5 and 6, each containing 16 pixels and using the implied default type (NEO_KHZ800 + NEO_GRB).

Can I connect multiple NeoPixel strips to the same Arduino pin?

In many cases, yes. All the strips will then show exactly the same thing. This only works up to a point though…four strips on a single pin is a good and reliable number. If you need more than that, individual NeoPixels can be used as buffers to “fan out” to more strips: connect one Arduino pin to the inputs of four separate NeoPixels, then connect each pixels’ output to the inputs of four strips (or fewer, if you don’t need quite that many). If the strips are 10 pixels long, declare the NeoPixel object as having 11 pixels. The extra “buffer” pixels will be at position #0 — just leave them turned off — and the strips then run from positions 1 through 10.

I'm getting the wrong colors. Red and blue are swapped!

When using through-hole 8mm NeoPixels (or V1 Flora pixels), use NEO_RGB for the third parameter in the Adafruit_NeoPixel declaration. For all other types of NeoPixels, use NEO_GRB.

Pixels Gobble RAM

Each NeoPixel requires about 3 bytes of RAM. This doesn’t sound like very much, but when you start using dozens or even hundreds of pixels, and consider that the mainstream Arduino Uno only has 2 kilobytes of RAM (often much less after other libraries stake their claim), this can be a real problem!

For using really large numbers of LEDs, you might need to step up to a more potent board like the Arduino Mega or Due. But if you’re close and need just a little extra space, you can sometimes tweak your code to be more RAM-efficient. This tutorial has some pointers on memory usage.
Last updated on 2015-04-01 at 08.20.24 AM Published on 2013-08-30 at 09.06.47 PM