module HardwareBase

  def self.register_device_type mod, sym
    @@device_registrations ||= {}
    @@device_registrations[sym] = mod
  end

end

module Servo
  include HardwareBase

  HardwareBase.register_device_type self, :servo

  def output_pin_setup(num,opts)
	#...do stuff...
  end
end

module I2C
  include HardwareBase

  HardwareBase.register_device_type self, :i2c

  def output_pin_setup(num,opts)
	#...do stuff...
  end
end

class ArduinoSketch
  include Servo
  include I2C

  def initialize
    puts @@device_registrations.inspect
  end
end

ArduinoSketch.new#.device_registrations.inspect