Server and user interface to control WS2801 RGB LED strips via SPI

Usage no npm install needed!

<script type="module">
  import wolkd from 'https://cdn.skypack.dev/wolkd';



Node.js server and user interface to control WS2801 RGB LED strips via SPI. Built to control wolk.bike, a bike skelter sound system cloud commisioned by Welcome to the Village 2015.

wolkd can display mathematical functions, frame-by-frame animations (and even animated GIFs!) on RGB LED strips, and can be controlled via a web interface — with your laptop, smartphone or tablet. wolkd lets you write animations in terms of either a pixel's LED strip index or x and y coordinates using a mapping file. And wolkd has a 256 color ANSI terminal debug mode!

wolkd works well in conjunction with LED Strip Mapper.

See http://wolk.bike for more photos!


git clone https://github.com/bertspaan/wolkd.git
cd wolkd
npm install

If your device has an SPI interface (Raspberry Pis have one!), you can install node-spi:

npm install spi

Please note: without node-spi, wolkd will run in console mode!

wolkd expects the environment variable WOLKD_CONFIG to point to the path of the wolkd configuration JSON file.

cp wolkd.example.config.json ~/wolkd.config.json
export WOLKD_CONFIG=/home/wolk/wolkd.config.json

wolkd's configuration and command line arguments are described in detail below.

To run wolkd, type:

node index.js

When running wolkd on your laptop and/or in console mode, the RGB LED output is mapped to the terminal:

User interface

After starting wolkd, a web interface to control wolkd and mix patterns is available on http://localhost:3000:


wolkd supports two kinds of patterns:

  1. Functions: functions are executed every frame for each active pattern
  2. Frames: frames are hard-coded arrays of pixel colors.


module.exports =  {
  title: 'Function',
  getPixel: function(beat, t, i, x, y) {
    // beat: beat number
    // t: frame number
    // i: pixel index
    // x: x coordinate of pixel, according to mapping
    // y: y coordinate of pixel, according to mapping
    return [r, g, b];


module.exports = {
  title: 'Frames',
  frames: [
      [0, 0, 0],     // Frame 1, pixel 1
      [255, 0, 0],   // Frame 1, pixel 2
      [0, 255, 0],   // Frame 2, pixel 1
      [255, 255, 0], // Frame 2, pixel 2

TODO: animated GIFs!


Each frame, wolkd outputs its pixel data to a screen. Currently, wolkd has two screens available: spi and console.

It's easy to add your own screens, by creating a JavaScript file in the screens directory.

exports.setPixel = function(pixel, r, g, b) {
  // Set RGB color of individual indexed pixel in buffer

exports.update = function update() {
  // Send buffer to screen, called each frame


wolkd uses a JSON mapping file to convert a pixel's LED strip index to its x and y coordinates (between 0 and 1). You can use LED Strip Mapper to generate such patterns from an SVG file.

You can find wolkd's mappings in the mappings directory


Autopilot is very smart and can create beautiful random patterns!


  "pixels": 100,                // Number of pixels on LED strip
  "framerate": 30,              // Framerate wolkd tries to achieve
  "bpm": 120,                   // Default BPM
  "framesPerBeat": 16,          // Frames per beat - constant if BPM changes
  "spi": {
    "device": "/dev/spidev0.0"  // SPI device
  "autopilot": {
    "enabled": true,            // Enable/disable [autopilot](#autopilot)
    "inputTimeout": 120000,     // Time in milliseconds before autopilot starts
                                //   after user input
    "patternTimeout": 60000     // Time after which autopilot changes patterns
  "mapping": "st-bree",         // Default [mapping file](#mappings)
  "screen": "spi",              // Default [screen](#screens)
  "hostname": "wolkd.local",    // Used by web interface
  "websocket": {
    "port": 8080                // Used by web interface
  "http": {
    "port": 3000                // Used by web interface

Command line arguments

You can override some of the options set in the configuration file with the following command line arguments:

Argument Example Description
--screen <screen> --screen console Choose screen
--mapping <mapping> --mapping wolk Choose mapping file
--autopilot <true|false> --autopilot false Enable or disable autopilot

Raspberry Pi

Instructions for installing wolkd on a Raspberry Pi:

server {
    listen 80;
    server_name wolk.local;
    location / {
        proxy_pass http://localhost:3000/;
  • sudo ln -s /etc/nginx/sites-available/veldnamen /etc/nginx/sites-enabled && sudo service nginx restart
  • Create wolkd daemon: http://www.slidequest.com/Taboca/70ang:
    1. sudo npm install -g forever
    2. sudo cp ./daemon/wolkd /etc/init.d/wolkd
    3. sudo chmod 755 /etc/init.d/wolkd
    4. sudo update-rc.d wolkd defaults


  • Language files/config for user interface
  • In UI, sliders should change when wolkd changes patterns/modifiers
  • Frame animations with configurable speed
  • Patterns either continuous (each frame) or per beat
  • Create programs, combinations of patterns that work well together
  • Add colors or images to buttons in user interface
  • Add modifiers which change hue/color through time
  • FFT audio analysis and beat detection using microphone
  • Add Open Pixel Control support
  • Send output to Fadecandy Controller board
  • Add websocket screen and HTML Canvas viewer

See also