Nerves.IO.Neopixel

Drive WS2812B “NeoPixel” RGB LED strips from a Raspberry Pi using Elixir!

This project was designed to make it easy to drive a string of AdaFruit NeoPixels from a Raspberry Pi using Nerves. The code would probably also work outside of Nerves with minor modifications to the Makefile, if you so desire.

Unfortunately, since the Raspberry Pi has 3.3V I/O outputs and the NeoPixels require 5V I/O input, a little piece of hardware is required. You can read more about this in my blog post about the project.

Installation

1. Add it to your list of dependencies in mix.exs:

   def deps do

    [{:nerves_io_neopixel, "~> 0.1.0"}]

   end

2. Ensure it is started before your application:

   def application do

    [applications: [:nerves_io_neopixel]]

   end

Usage

Supervision trees and an Elixir Port are used to maintain fault-tolerance when interfacing with the low-level driver, which is written in C. To drive an NeoPixel strip, you just have to configure which GPIO pin to use and how many NeoPixels are in the strip using the Nerves.IO.NeoPixel.setup function. Once you had a pid from the setup function, you can call the Nerves.IO.Neopixel.render function with the pid and a binary structure representing the pixel data.

Here’s a simple example:

alias Nerves.IO.Neopixel
{:ok, pid} = Neopixel.setup pin: 18, count: 3
Neopixel.render(
  pid,
  <<
    255, 0, 0, # LED 1: red
    0, 255, 0, # LED 2: green
    0, 0, 255  # LED 3: blue
  >>
)