Node Pixel

The purpose of this library is to provide a node js interface for addressable RGB LEDs. Most commonly these are known as Neo Pixels (if you shop at Adafruit) however any WS2812b addressable LED should work with this library.

The current iteration supports two methods of set up:

• a custom version of firmata that provides an interface to talk to the "pixels".
• an I2C "backpack" using an arduino pro mini or nano that provides the interface and control of the pixels and then the IO controller talks to this backpack over I2C messages.

The pixel library can be used with both Johnny-Five or stock Node Firmata and can be used by any board that provides an IO interface with I2C support such as a Raspberry PI.

Both fimwares are provided in this repo in the firmware/build directory.

Getting help

If you need some help getting your pixel strip working with johnny five jump into the Gitter Chat or reach out to ajfisher on twitter or just raise an issue here.

Installation

Installation of both backpack and custom firmata are covered in detail in the Installation Guide.

Short version for node-pixel custom firmata.

npm install node-pixel
npm install -g nodebots-interchange

Plug in your arduino

interchange install git+https://github.com/ajfisher/node-pixel -a uno --firmata

Note that on windows, you may need to explictly pass a port to flash due to the way com ports work. eg:

interchange install git+https://github.com/ajfisher/node-pixel -a uno -p COM3 --firmata

A note on multiple strips

Multiple led strips on one arduino or backpack are supported up to a maximum of 8 individual strips (8 pins in use at once). Each strip can be different lengths but you can only have a maximum of 192 pixels for Firmata and about 500 pixels for the backpack version.

Multiple strips connected to a single board or backpack are for the purposes of node-pixel considered to be a single strip and are joined together in sequence in the order that you define them.

On a backpack, the strips are defined sequentially from pin 0-7 on the backpack.

On an arduino, each strip can be defined with an individual pin which doesn't need to be sequential (eg you can use pin 3, then pin 9, then pin 7).

One thing to note is that the timings on these strips are quite tight and you will reach an upper limit of how much data you can push to the board controlling the pixels (all that RGB data going over the wire) and the sheer number of pixels you can refresh quickly (each pixel is written "in turn"). As such, you may run into some blocking conflicts. These are discussed in this issue.

Pixel API

The Pixel API is provided below.

Strip

A sequence of LEDs collected together is called a strip. A strip has a controller to tell it to use the custom firmata or I2C backpack. A strip can be a single physical strip in which case a single pin and length can be provided. Otherwise it is made up of multiple physical strips, each of which have their own pin and length and are composed together into order by using the strips array as part of the definition of the object.

For the purposes of interaction however, once a strip is defined, it is all one logical unit and the firmware will take care of writing data in the right order, performing optimisations for strips that have or haven't changed and writing in sequence or parallel as appropriate.

Parameters

• options An object of property parameters

(1) A board or firmata object is required but only one of these needs to be set.

(2) If using a backpack use an array of lengths eg [8, 8, 8] which would set pins 0, 1 & 2 on the backpack to have strips of length 8 each on them.

(3) If using custom firmata then use an array of objects eg [ {pin: 4, length: 8}, {pin: 10, length: 8}, {pin: 11, length: 8} ] which would set pins 4, 10 & 11 to have strips of length 8 on each of them.

(4) If not supplied, it is assumed a strips array will be provided with a pin parameter for each object in the array.

(5) If not supplied, it is assumed a strips array will be provided with a length parameter for each object in the array.

(6) If supplied it will apply to all strips unless overridden selectively in the strips array eg [ {color_order: pixel.COLOR_ORDER.RGB}, ..]

(7) Currently set to 1.0 to maintain current behaviour. Will move to 2.8 default in version 0.10.

Properties

• length - number of pixels in the strip
• gamma - the currently set gamma for the strip

Events

• onready() - emits when the strip is configured.
• onerror() - returns the error that occurred.

Examples

Johnny-Five instantiation

pixel = require("node-pixel");
five = require("johnny-five");

var board = new five.Board(opts);
var strip = null;

board.on("ready", function() {

    strip = new pixel.Strip({
        board: this,
        controller: "FIRMATA",
        strips: [ {pin: 6, length: 4}, ], // this is preferred form for definition
        gamma: 2.8, // set to a gamma that works nicely for WS2812
    });

    strip.on("ready", function() {
        // do stuff with the strip here.
    });
});

Firmata instantiation

pixel = require("node-pixel");
var firmata = require('firmata');

var board = new firmata.Board('path to usb',function(){

    strip = new pixel.Strip({
        pin: 6, // this is still supported as a shorthand
        length: 4,
        firmata: board,
        controller: "FIRMATA",

    });

    strip.on("ready", function() {
        // do stuff with the strip here.
    });
});

Johnny Five with backpack

pixel = require("node-pixel");
five = require("johnny-five");

var board = new five.Board(opts);

board.on("ready", function() {
    strip = new pixel.Strip({
        board: this,
        controller: "I2CBACKPACK",
        strips: [4, 6, 8], // 3 physical strips on pins 0, 1 & 2 with lengths 4, 6 & 8.
    });

    strip.on("ready", function() {
        // do stuff with the strip here.

    });
});

Note that Johnny-Five uses the board option and firmata uses the firmata option. This is because the pixel library supports a Board capable of presenting an IO interface. The library will work out the right thing to do based on the board being passed and the controller being set.

Methods

show();

The show method should be called at the point you want to "set" the frame on the strip of pixels and show them.

Note that when this method is called it will trigger the process that writes the frame to the strips. If you have a very long strip of LEDs this may take some time (assume 0.5ms per pixel) and is a blocking operation in most cases.

This gives you an upper limit as to how many frames you can drive per second.

Example

// ... make pixel modifications

strip.show(); // make the strip latch and update the LEDs

Addressable LEDs work by clocking data along their entire length and so you make the various changes you want to the strip as you need to without triggering the display (like a frame buffer). Once you're ready you can then call show() to propagate this data through the LEDs and display the frame.

off();

All LEDs on the strip can be turned off by using the .off() method. This effectively clears the current colours set on the strip.

.clear() is also aliased to the same method.

Example

strip.off(); // turn the strip off / clear pixel colours

color( colourstring );

All LEDs on the strip can be set to the same colour using the .color() method.

.colour() is also aliased to the same method.

Parameters

• colourstring A String as a standard HTML hex colour or a CSS colour name, or a CSS rgb(r, g, b) value used to specify the colour of the strip. Alternatively an Array object as an rgb value eg [r, g, b]

Examples

Set strip using a hex value

strip.color("#ff0000"); // turns entire strip red using a hex colour
strip.show();

Update strip using a named CSS colour

strip.colour("teal"); // sets strip to a blue-green color using a named colour
strip.show();

You can also use CSS RGB values

strip.color("rgb(0, 255, 0)"); // sets strip to green using rgb values
strip.show();

Or set using an array of RGB values

strip.color([255, 255, 0]); // Sets strip using an array
strip.show();

shift( amt, direction, wrap );

All LEDs on the strip can be shifted along the strip forwards or backwards by the given amount. This is very useful for long strip animation when you're moving the whole strip by a pixel in one direction each frame and means you don't have to send an update of framelength messages

Parameters

• amt A Number representing the number of pixels you want everything to shift by.
• direction Either Pixel.FORWARD or Pixel.BACKWARD value which determines direction of travel. Forward direction is in the flow index values (ie index 1->2 etc).
• wrap a Boolean representing whether to wrap the values that go off the "end" of the strip back around to the start - useful for circular displays.

Example

strip.pixel(0).color("#000");
strip.pixel(1).color("red");
strip.shift(1, pixel.FORWARD, true);
strip.pixel(1).color; // will now be nothing
strip.pixel(2).color; // will now be red.

pixel( address );

Individual pixels can be addressed by the pixel method using their address in the sequence.

Note that if you have two physical strips of 8 and 10 then pixel(10) will be the third pixel on the second physical strip.

Parameters

• address A Number indexing the pixel you want. Returns a Pixel object.

Example

var p = strip.pixel(1); // get the second LED. p is now a Pixel object

Pixel

A pixel is an individual element in the strip. It is fairly basic and it's API is detailed below.

Methods

color( color string )

Colors work exactly the same way on individual pixels as per strips so see the strip.color reference above.

.colour() is aliased to this method as well.

Parameters

• color string A String providing the hex colour, CSS colour name or CSS rgb() values to be used to set the individual pixel a certain colour. You can also pass in an Array object that is a set of RGB values as [r, g, b].

Examples

var p = strip.pixel(1);     // get second LED
p.color("#0000FF");         // set second pixel blue.

p = strip.pixel(2);         // get third LED
p.colour("orange");          // set third pixel red/yellow

p = strip.pixel(3);         // get fourth LED
p.color("rgb(0, 255, 0)");  // set fourth LED green

p = strip.pixel(4);         // get fifth LED
p.color([255, 0, 255]);     // set fifth LED magenta

color()

Returns an object representing the color of this pixel with the shape below.

.colour() is aliased to this method as well.

Parameters

• none

Shape

{
    r: 0,               // red component
    g: 0,               // green component
    b: 0,               // blue component
    hexcode: "#000000", // hexcode of color
    color: "black",     // keyword name of color if matching
    rgb: [0,0,0],       // RGB component array
}

Example

Get a pixel, set it's colour and then query it's current state.

var p = strip.pixel(1); // get second LED

p.color("#0000FF"); // set second pixel blue.

p.color(); // returns {r:0, g:0, b:255, hexcode:"#0000ff", color:"blue", rgb[0,0,255]}

off()

Turns the pixel to it's off state.

.clear() is also aliased to this method.

Example

Set a pixel value to off

var p = strip.pixel(1); // get second LED
p.off(); // turn it off
p.color(); // returns {r: 0, g: 0, b: 0, hexcode:"#000000", color:"black", rgb: [0,0,0]}
strip.show(); // pixel will be off

Detailed examples with circuits

• Basic single strip using custom firmata
• Basic single strip using Johnny Five Firmata
• Single strip using Johnny Five over I2C Backpack
• Mutiple strips using Johnny Five over firmata
• Multiple strips using Johnny Five over I2C Backpack
• Controlling a panel and using strip.color()
• Static rainbow with a single strip
• Dynamic rainbow over a single strip
• Dynamic rainbow over multiple strips
• Random pixels flowing down multiple strips

TODO and roadmap

This library is under active development and planned modifications are:

• Provide methods of having different shapes to the strips including 3D
• Prvide method of pixel selection using polar coordinates for circles and hexes