node-mcp23017

Node.js library for the I2C I/O Expander MCP23017 on a Raspberry Pi

It currently supports reading, writing and changing the pull-up resistor of the GPIOs.

The module tries to mimic the Arduino-Syntax

##Installation

install via npm. just type the following in the terminal/console

npm install node-mcp23017 --save

Raspberry Pi Setup

In order to use this module with the Raspberry Pi running Raspbian you have to enable to stuff

$ sudo vi /etc/modules

Add these two lines

i2c-bcm2708
i2c-dev

$ sudo vi /etc/modprobe.d/raspi-blacklist.conf

Comment out blacklist i2c-bcm2708

#blacklist i2c-bcm2708

Load kernel module

$ sudo modprobe i2c-bcm2708

Make device writable

sudo chmod o+rw /dev/i2c*

Usage

NOTE

Pins are numbered from 0-15 where 0-7 is register A and 8-15 is register B

var MCP23017 = require('node-mcp23017');

var mcp = new MCP23017({
  address: 0x20,//default: 0x20
  device: 1,    // 1 for '/dev/i2c-1' on model B | 0 for '/dev/i2c-0' on model A
                // 'ls /dev/i2c*' to find which device file / number you should use
  debug: true   //default: false
});

/*
  By default all GPIOs are defined as INPUTS.
  You can set them all the be OUTPUTs by using the pinMode-Methode (see below),
  You can also disable the debug option by simply not passing it to the constructor
  or by setting it to false
*/

//set all GPIOS to be OUTPUTS
for (var i = 0; i < 16; i++) {
  mcp.pinMode(i, mcp.OUTPUT);
  //mcp.pinMode(i, mcp.INPUT); //if you want them to be inputs
  //mcp.pinMode(i, mcp.INPUT_PULLUP); //if you want them to be pullup inputs
}

mcp.digitalWrite(0, mcp.HIGH); //set GPIO A Pin 0 to state HIGH
mcp.digitalWrite(0, mcp.LOW); //set GPIO A Pin 0 to state LOW

/*
  to read an input use the following code-block.
  This reads pin Nr. 0 (GPIO A Pin 0)
  value is either false or true
*/
mcp.digitalRead(0, function (pin, err, value) {
  console.log('Pin 0', value);
});

Example (Blink 16 LEDs)

see examples folder

var MCP23017 = require('node-mcp23017');

var mcp = new MCP23017({
  address: 0x20, //all address pins pulled low
  device: 1, // Model B
  debug: false
});

/*
  This function blinks 16 LED, each hooked up to an port of the MCP23017
*/
var pin = 0;
var max = 16;
var state = false;

var blink = function() {
  if (pin >= max) {
    pin = 0; //reset the pin counter if we reach the end
  }

  if (state) {
    mcp.digitalWrite(pin, mcp.LOW); //turn off the current LED
    pin++; //increase counter
  } else {
    mcp.digitalWrite(pin, mcp.HIGH); //turn on the current LED
    console.log('blinking pin', pin);
  }
  state = !state; //invert the state of this LED
};

//define all gpios as outputs
for (var i = 0; i < 16; i++) {
  mcp.pinMode(i, mcp.OUTPUT);
}

setInterval(blink, 100); //blink all LED's with a delay of 100ms

TODO

• implement interrupt handling

Acknowledgement

some parts are derived from the module https://github.com/x3itsolutions/mcp23017 by x3itsolutions (Fabian Behnke)