rprieto / node-max7221

Node.js GPIO abstraction for the MAX7221 driver chip (LED matrix), for use on a Raspberry PI

node-max7221

Node.js GPIO abstraction for the MAX7221 driver chip (LED matrix), for use on a Raspberry PI. Built by Brad Ward, James Ottaway, and Romain Prieto at CampJS 2013

Requirements

• Raspberry PI
• LED Matrix
• MAX7221 display driver chip (http://www.maximintegrated.com/datasheet/index.mvp/id/1339)
• Wiring components (breadboard, jumper wires, resistors, capacitors)

Or a pre-made LED matrix kit:

On the Raspberry PI:

• Install Node.js
• Install GPIO admin so you don't need to run Node as root

Show me the code

var max7221 = require('node-max7221');

// which GPIO pins are wired to the MAX7221 driver (see diagram in /docs folder)
// can be any valid GPIO pins
max7221.configure({ dataIn: 25, load: 8, clock: 7 });

max7221.open(function() {

    // write a single bitmap
    max7221.write(bitmap);
    
    // start a sequence or some scrolling text
    max7221.sequence([bitmap, bitmap, bitmap], 500);
    max7221.scroll([bitmap, bitmap, bitmap], 500);
    
    // stop a running sequence/scroll
    max7221.stop();

});

process.on('SIGTERM', max7221.close);

Bitmaps can be loaded or defined easily:

// predefined letters numbers & symbols
max7221.ascii['a']
max7221.ascii['3']
max7221.ascii['.']

// syntactic sugar for a list of ascii characters
max7221.text('hello world!')

// make an 8x8 bitmap from arrays (ex: ndarray)
max7221.matrix([
    [1,0,1,0,1,0,1,0],
    [0,1,0,1,0,1,0,1],
    [1,0,1,0,1,0,1,0],
    [0,1,0,1,0,1,0,1],
    [1,0,1,0,1,0,1,0],
    [0,1,0,1,0,1,0,1],
    [1,0,1,0,1,0,1,0],
    [0,1,0,1,0,1,0,1]
]);

// make an 8x8 bitmap from strings (easy to read in code)
max7221.matrix([
    '  1111  ',
    ' 111111 ',
    '111  111',
    '11    11',
    '11    11',
    '111  111',
    ' 111111 ',
    '  1111  ',
]);

// load a whole array of bitmaps at once
max7221.matrices([
    '  1111  ',  '   11   ',  '11111111',
    ' 111111 ',  '   11   ',  ' 111111 ',
    '111  111',  '   11   ',  '  1111  ',
    '11    11',  '11111111',  '   11   ',
    '11    11',  '11111111',  '   11   ',
    '111  111',  '   11   ',  '  1111  ',
    ' 111111 ',  '   11   ',  ' 111111 ',
    '  1111  ',  '   11   ',  '11111111',
]);

Running the samples

On your Raspberry PI:

git clone [e-mail]:rprieto/node-max7221.git
cd node-max7221
npm install --production

node examples/helloworld.js
node examples/shapes.js

Notes

The write function is synchronous. GPIO works by writing to the file system, and current Node.js limitations mean fs.writeFileSync() is an order of magnitude faster than fs.writeFile() when writing little content.

This module only handles 1 color for now.