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Introduction

The MCP23017 is an I/O expander chip. It has 16 GPIO pins which you can control using an I2C interface using two pins from a Raspberry Pi, plus a power source and sink (which can also come from the Pi). It's not quite as simple as directly controlling the Pi's GPIO pins, but it's not complicated, either.

You need to install i2c-tools, which is probably in your distribution's package manager. You also need a kernel with I2C support; you might need to modprobe i2c-dev. It would presumably be possible to do without either of these things, and bitbang the I2C protocol over GPIO, but I don't understand the protocol well enough to try.

On pin numbering: if you like, you can refer to the datasheet for the MCP23017. There's a small dot in one corner of the chip, with a semi-circular cut-out at that end. The pin near

For Windows:

Download and install Putty
Connect your USB to UART adapter from your computer to your Nano Pi Neo Air (or any COM device)
Make sure you connect TX>RX and RX>TX (Sending/Receiving), otherwise both your devices are talking at the same time and neither one is being heard.
On Windows OS, pull up the Device Manager
- Run Windows (WinKey+R) and type in devmgmt.msc

	# Free RESTful interface for your Ruby objects with Rackable
	# http://github.com/madx/rackable/tree/master
	#
	# + Free HTTP caching with rack-cache
	# http://github.com/rtomayko/rack-cache/tree/master

	require 'rackable'
	require 'rack/cache'

	APP_ROOT = File.dirname(__FILE__)

	/* Ismael Celis 2010
	Simplified WebSocket events dispatcher (no channels, no users)

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	// string. Oh yeah, you have to pass the result of ghettoTmpl to eval. :)

	function ghettoTmpl(data, str) {
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	/**
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	* To verify that a CSS property is supported (or any of its browser-specific implementations)
	*
	* @param string p - css property name
	* [@param] bool rp - optional, if set to true, the css property name will be returned, instead of a boolean support indicator
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	#!/usr/bin/env ruby
	# encoding: UTF-8

	$VERBOSE = true # -w
	$KCODE = "U" if RUBY_VERSION < "1.9" # -KU

	require 'optparse'
	require 'socket'
	require 'fileutils'

	#!/bin/sh

	### BEGIN INIT INFO
	# Provides: mpd-autoplay
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	* Use like this: <gist data-username="brandonb927" data-id="4138162" data-file="gists2.js"><a href="https://gist.github.com/brandonb927/4138162#file_gists2.js">Gist</a></gist>
	* UPDATED 02/06/2013: Github implemented Namespaced Gists a few hours ago, which means gist.github.com/4149074 now redirects to gist.github.com/brandonb927/4149074 and I have updated the gist to reflect this new format
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	(function(){
	var gists = document.getElementsByTagName('gist');