Servo Animator

require 'rubygems'
require 'ruby-audio'

# Info at http://www.horrorseek.com/home/halloween/wolfstone/Motors/svoint_RCServos.html
class ServoAnimation
  SampleRate = 48000 # samples per second
  RePulse = 200 # hertz
  CentreWidth = 1.5 # mSec
  ScaleWidth = 0.9 # mSec
  PulseEvery = SampleRate / RePulse
  DefaultWait = 0.5
  
  def self.polarity= polarity
    @polarity = polarity
  end
  
  def self.inherited stay_classy; stay_classy.begin; end
  
  def self.begin;
    @file = "#{self.name}.wav"
    @info = RubyAudio::SoundInfo.new :channels => 1, :samplerate => SampleRate, :format => RubyAudio::FORMAT_WAV|RubyAudio::FORMAT_PCM_16
    @snd = RubyAudio::Sound.open(@file, 'w', @info)
    @angle = 0
    @polarity = +1.0
  end
  
  # Stop sending commands, letting the servo go limp, for a duration
  def self.limp seconds = DefaultWait
    @angle = nil
    buffer = RubyAudio::Buffer.new('float', PulseEvery)
    buffer.size.times { |i| buffer[i] = 0.0 }
    
    (seconds * RePulse.to_f).round.times do
      @snd.write buffer
    end
  end
  
  # Wait for a duration, holding the servo at the current angle (or limp if no angle set yet)
  def self.wait seconds = DefaultWait
    return self.limp(seconds) unless @angle
    
    buffer = RubyAudio::Buffer.new('float', PulseEvery)
    threshold = (CentreWidth + (ScaleWidth * @angle)) * 0.001 * SampleRate
    buffer.size.times do |i|
      buffer[i] = ((i < threshold) && @polarity) || 0.0
    end
    
    (seconds * RePulse.to_f).round.times do
      @snd.write buffer
    end
  end
  
  def self.set angle
    @angle = angle
  end
end

# Should make servo go all the way left, then all the way right, then go limp for one second!
class Wiggle < ServoAnimation
  set -1.0
  wait 2.0
  set +1.0
  wait 2.0
  limp 1.0
end