poll_server.rb

require 'serialport'
require 'pry'
require 'net/http'
require 'json'

class Arduino
  # Params for serial port
  PORT      = "/dev/tty.usbmodemfd121"
  DATA_BITS = 8
  STOP_BITS = 1
  BAUD_RATE = 9600
  PARITY    = SerialPort::NONE
  
  def initialize
    @sp = SerialPort.new(PORT, BAUD_RATE, DATA_BITS, STOP_BITS, PARITY)
  end
  
  def write_to_pin(number, high = true)
    @sp.write(?P + ("A".ord + number - 1).chr + (high ? ?1 : ?0 ) + "\r\n")
  end
  
  def led_on
    write_to_pin(13, true)
  end
  
  def led_off
    write_to_pin(13, false)
  end
  
  def turn_servo(angle)
    sign = angle < 0 ? ?- : ?+
    turn_char = angle.abs
    @sp.write(?S + turn_char.chr + sign + "\r\n")
  end
end

arduino = Arduino.new

uri = URI.parse("http://ec2-50-19-60-252.compute-1.amazonaws.com/query.json")

current_state = {:led => false, :servo => 0}
while true do
  response = Net::HTTP.get_response(uri)
  result   = JSON.parse(response.body)
  
  if result
    if result["led"] != current_state[:led]
      current_state[:led] = result["led"]
      puts "Change detected! LED is now #{current_state[:led] ? "on" : "off"}"
      
      current_state[:led] ? arduino.led_on : arduino.led_off
    end
    
    if result["servo"] != current_state[:servo]
      current_state[:servo] = result["servo"]
      arduino.turn_servo(current_state[:servo])
    end
  end
  
  sleep 2
end