Drive NeoPixels in Docker on Raspberry Pi

In our last blog post we showed you how to interact with the GPIO ports and how to turn on one LED. Now for some more magic lights we create a little Node.js application that drives a NeoPixel LED strip from Adafruit in a Docker container.

Thanks to the latest improvements now both Raspberry Pi B/B+ and the new Pi 2 B can drive the NeoPixel LED strips from Adafruit with just a level shifter. So it’s time to put this into Docker for easier deployment.

The NeoPixel (or WS2812) LED’s are programmable RGB LED’s that receive their RGB value with a single serial wire.

Wiring

Let’s have a look at the wiring first. The Raspberry Pi can create the serial signal on GPIO Pin 18 trough PWM/DMA. But the signal level has to be shifted from 3.3V to 5V for the LED strip. I have used a Adafruit Level Shifter Breakout Board, but a 74AHCT125 level converter could be used as well.

wiring diagram

Do not power the NeoPixels directly from your Raspberry Pi as the 5V output could not source enough current to light many pixels. This could damage your Raspberry Pi! For my tests with only eight pixels it is ok to use the 5V from the Pi, but be warned!

The code

First we create the package.json file with a dependency to the rpi-ws281x-native Node.js module that supports all Raspberry Pi versions to drive the NeoPixels.

package.json

{
  "name": "rpi-node-neopixel-example",
  "private": true,
  "version": "0.0.1",
  "description": "Node.js NeoPixel app in docker",
  "author": "hypriot.com",
  "dependencies": {
    "rpi-ws281x-native": "0.4.0"
  }
}

server.js

Now we implement a Node.js sample that does some color magic. We have reduced the brightness of the LED’s a little bit.

var ws281x = require('rpi-ws281x-native');

var NUM_LEDS = parseInt(process.argv[2], 10) || 8,
    pixelData = new Uint32Array(NUM_LEDS);

var brightness = 128;

ws281x.init(NUM_LEDS);


var lightsOff = function () {
  for (var i = 0; i < NUM_LEDS; i++) {
    pixelData[i] = color(0, 0, 0);
  }
  ws281x.render(pixelData);
  ws281x.reset();
}

var signals = {
  'SIGINT': 2,
  'SIGTERM': 15
};

function shutdown(signal, value) {
  console.log('Stopped by ' + signal);
  lightsOff();
  process.nextTick(function () { process.exit(0); });
}

Object.keys(signals).forEach(function (signal) {
  process.on(signal, function () {
    shutdown(signal, signals[signal]);
  });
});

// ---- animation-loop
var offset = 0;
setInterval(function () {
  for (var i = 0; i < NUM_LEDS; i++) {
    pixelData[i] = wheel(((i * 256 / NUM_LEDS) + offset) % 256);
  }

  offset = (offset + 1) % 256;
  ws281x.render(pixelData);
}, 1000 / 30);

console.log('Rainbow started. Press <ctrl>+C to exit.');

// generate rainbow colors accross 0-255 positions.
function wheel(pos) {
  pos = 255 - pos;
  if (pos < 85) { return color(255 - pos * 3, 0, pos * 3); }
  else if (pos < 170) { pos -= 85; return color(0, pos * 3, 255 - pos * 3); }
  else { pos -= 170; return color(pos * 3, 255 - pos * 3, 0); }
}

// generate integer from RGB value
function color(r, g, b) {
  r = r * brightness / 255;
  g = g * brightness / 255;
  b = b * brightness / 255;
  return ((r & 0xff) << 16) + ((g & 0xff) << 8) + (b & 0xff);
}

Dockerfile

The Dockerfile is very simple here as we use the onbuild version of our hypriot/rpi-iojs Docker image.

FROM hypriot/rpi-iojs:onbuild

Build the Docker image

We now have all parts together and are ready to build the docker image with this command

$ docker build -t node-neopixel .

Run the Docker container

Now it is time to turn on the NeoPixel LED’s by running the container

$ docker run --cap-add SYS_RAWIO --device /dev/mem -d node-neopixel

On a Raspberry Pi 2 you have to give the container more privileges. So you have to use this command instead

$ docker run --privileged -d node-neopixel

Let there be lights!

You can find the complete Node.js example on GitHub at https://github.com/hypriot/rpi-node-neopixel-example.

Conclusion

Now you are ready to start your NeoPixel project on your Raspberry Pi and deploy it with Docker.

To learn more about NeoPixels head over to the excellent Adafruit’s NeoPixel Ɯberguide.

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