Open Pixel Control protocol
Last updated 4 years ago by parshap .
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Open Pixel Control

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Control lights using the Open Pixel Control protocol.

Module Scope

This module handles binary encoding and decoding of the Open Pixel Control protocol and provides a virtual address space for pixels.

This module was created to control Fadecandy devices, but it should work as a generic tool to create Open Pixel Control messages.


This module provides three components:

  • Encoder: Write binary messages
  • Decoder: Parse binary messages
  • Strand: Model of a strand of pixels and virtual address space


// Create TCP connection to Open Pixel Control server
var Socket = require("net").Socket;
var socket = new Socket();

// Create an Open Pixel Control stream and pipe it to the server
var createOPCStream = require("opc");
var stream = createOPCStream();

// Create a strand representing connected lights
var createStrand = require("opc/strand");
var strand = createStrand(512); // Fadecandy has 512 addresses
var left = strand.slice(0, 64); // Fadecandy pin 0
var right = strand.slice(64, 128); // Fadecand pin 1
// Set all left pixels to red and right to blue
for (var i = 0; i < 64; i++) {
  left.setPixel(i, 255, 0, 0);
  right.setPixel(i, 0, 0, 255);

// Write the pixel colors to the device on channel 0
stream.writePixels(0, strand.buffer);


var createStream = require("opc");

var stream = createStream()

Creates a stream that emits Open Pixel Control protocol messages.

stream.writePixels(channel, pixels)

Emits a set pixel colors command message with the color data in the pixels buffer.


Emits a Fadecandy set global color correction command message with the given config object.

stream.writeMessage(channel, command, data)

Emits a generic Open Pixel Control message. Data should be a buffer.


var createStrand = require("opc/strand");

var strand = createStrand(length)

Create a strand object representing a series of length pixels. The strand provides a strand.setPixel() function to set the color of each pixel.

Pixel state is stored in buffer (strand.buffer) in Open Pixel Control format (i.e., used in the data block of a set pixel color command).

strand.setPixel(index, r, g, b)

Set color at index to the given rgb value.


Return an array representing the rgb color value at index (e.g., [255, 0, 105]).

strand.slice(start, end)

Returns a new strand which references the same state as the old, but offset and cropped by the start and end indexes.

Modifying the new strand slice will modify the original strand!


Binary data representing the strand's pixel colors. The size of the buffer will be strand.length * 3 bytes.


The number of pixels in the strand.


var createParser = require("opc/parser");
var createStrand = require("opc/strand");

require("net").createServer(function(connection) {
  connection.pipe(createParser()).on("data", function(message) {
    console.log("  Channel:", message.channel);
    console.log("  Command:", message.command);
    console.log("  Data length:", message.data.length);

    // Read pixel colors
    if (message.command === 0) {
      var strand = createStrand(message.data);
      for (var i = 0; strand.length < i; i++) {
        console.log("  Pixel", i, strand.getPixel(i));

var parser = createParser()

Create a transform stream that parses binary data written to it an emits Open Pixel Control messages. Message objects have the following properties:

  • channel: The channel id
  • command: The command id
  • data: A buffer containing the message data


npm install opc

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