diff --git a/README.md b/README.md
new file mode 100644
index 0000000..18d992d
--- /dev/null
+++ b/README.md
@@ -0,0 +1,20 @@
+
+# RPi Theremin
+
+This is a quick-n-dirty Theremin daemon for use on the RaspberryPi.
+
+It is designed to be used with a couple of these distance sensors:
+
+	https://www.adafruit.com/product/4007
+
+Use 'raspi-config' to configure your default sound output (HDMI, 3.5", etc).
+
+
+This is intended to be run from daemontools or runit.  Quick setup:
+
+	# apt install ruby fluidsynth runit
+	# gem install -Ng
+	# ln -s /path/to/here/theremin /etc/service
+	# ln -s /path/to/here/fluidsynth /etc/service
+
+
diff --git a/fluidsynth/run b/fluidsynth/run
new file mode 100755
index 0000000..dce152e
--- /dev/null
+++ b/fluidsynth/run
@@ -0,0 +1,12 @@
+#!/bin/sh
+#
+# Run fluidsynth as a server, with some more dedicated CPU "oomph".
+#
+
+exec 2>&1
+exec fluidsynth -v -n -i -s \
+	-a alsa -c2 -z1024 \
+	-o synth.cpu-cores=4 \
+	-o audio.realtime-prio=95 \
+	-o audio.alsa.device=hw:0
+
diff --git a/gem.deps.rb b/gem.deps.rb
new file mode 100644
index 0000000..f9e1575
--- /dev/null
+++ b/gem.deps.rb
@@ -0,0 +1,4 @@
+source 'https://rubygems.org/'
+
+gem 'configurability', '~> 4.2'
+
diff --git a/theremin/Theremin.sf2 b/theremin/Theremin.sf2
new file mode 100644
index 0000000..4770055
Binary files /dev/null and b/theremin/Theremin.sf2 differ
diff --git a/theremin/config.yml b/theremin/config.yml
new file mode 100644
index 0000000..3131140
--- /dev/null
+++ b/theremin/config.yml
@@ -0,0 +1,18 @@
+# -*- ruby -*-
+# vim: set et sta sw=2 :
+
+---
+logging:
+  __default__: info (color)
+  theremin: debug (color)
+
+theremin:
+  pitch_trigger: 16
+  font: /usr/share/sounds/sf2/FluidR3_GM.sf2
+  glide: 1
+  slew: 0
+  sample_interval: 0.1
+  reverb: false
+  chorus: false
+  instrument_index: 29
+
diff --git a/theremin/lib/fluidsynth.rb b/theremin/lib/fluidsynth.rb
new file mode 100644
index 0000000..d6fd84c
--- /dev/null
+++ b/theremin/lib/fluidsynth.rb
@@ -0,0 +1,187 @@
+# -*- ruby -*-
+# vim: set noet sta sw=4 ts=4 :
+
+require 'socket'
+require 'configurability'
+require 'loggability'
+
+
+# Communicate with a running FluidSynth daemon via it's TCP socket API.
+#
+class FluidSynth
+	extend Configurability,
+		Loggability
+
+	# The default host for the fluidsynth server.
+	DEFAULT_HOST = 'localhost'
+
+	# The default port for the fluidsynth server.
+	DEFAULT_PORT = 9800
+
+
+	# Loggability API
+	log_as :fluidsynth
+
+	# Configuration API
+	#
+	configurability( :fluidsynth ) do
+
+		##
+		# How many simultaneous notes can play.  Keep low for better CPU.
+		setting :polyphony, default: 6
+
+		##
+		# Reverb amount.
+		setting :reverb_size, default: 0.9
+
+		##
+		# Reverb gain level.
+		setting :reverb_gain, default: 0.7
+
+		##
+		# Chorus depth.
+		setting :chorus_depth, default: 64.0
+
+		##
+		# Chorus gain level.
+		setting :chorus_gain, default: 1.5
+	end
+
+
+	def initialize( host=DEFAULT_HOST, port=DEFAULT_PORT )
+		@host = host
+		@port = port
+		@lastnote = nil
+		@velocity = 80
+	end
+
+	# The TCP socket to fluidsynth.
+	attr_reader :socket
+
+	# The previous note played, to enable glides.
+	attr_reader :lastnote
+
+	# The current velocity to play new notes at.
+	attr_accessor :velocity
+
+
+	### Open the TCP socket to the synth and perform initial setups.
+	###
+	def connect
+		@socket = TCPSocket.new( @host, @port )
+
+		self.setup_effects
+		self.polyphony( self.class.polyphony )
+	end
+
+
+	### Setup polyphony amount.
+	###
+	def polyphony( val )
+		self.send "synth.polyphony #{val}"
+	end
+
+
+	### Stop all notes and reset effects.
+	###
+	def panic
+		self.send "reset"
+	end
+
+
+	### Alter the default volume.
+	###
+	def gain( level )
+		self.send "gain #{level}"
+	end
+
+
+	### Turn glide (portamento) on or off.  Val is an integer that
+	### represents 128ms.  4 == 512ms.
+	###
+	def glide( val )
+		if val.zero?
+			self.send "cc 0 68 0"
+			self.send "cc 0 65 0"
+			self.send "cc 0 5 0"
+		else
+			self.send "setlegatomode 0 1"
+			self.send "cc 0 68 127" # legato
+			self.send "cc 0 65 127" # portamento
+			self.send "cc 0 5 #{val}"
+		end
+	end
+
+
+	### Play a midi +note+ at +velocity+, then silence the previous note.
+	### (This allows portamento to function if enabled.)
+	###
+	def playnote( note, velocity=self.velocity )
+		return if @lastnote == note
+		self.send "noteon 0 #{note} #{velocity}"
+		self.stopnote
+		@lastnote = note
+	end
+
+
+	### Silences the previous note played.
+	###
+	def stopnote
+		return unless @lastnote
+		self.send "noteoff 0 #{@lastnote}"
+	end
+
+
+	### Selects an instrument +index+ within the currently loaded sf2 for channel 0.
+	###
+	def instrument( index )
+		self.send "select 0 1 0 #{index}"
+	end
+
+
+	### Loads a resource (sf2, etc) from +path+.
+	###
+	def load( path )
+		self.send "load #{path}"
+	end
+
+
+	### Enable/disable reverb.
+	###
+	def reverb( toggle=true )
+		toggle = toggle ? 1 : 0
+		self.send "set synth.reverb.active #{toggle}"
+	end
+
+
+	### Enable/disable chorus.
+	###
+	def chorus( toggle=true )
+		toggle = toggle ? 1 : 0
+		self.send "set synth.chorus.active #{toggle}"
+	end
+
+
+	#########
+	protected
+	#########
+
+	### Initial effect setup.
+	###
+	def setup_effects
+		self.send "set synth.reverb.room-size 0.9"
+		self.send "set synth.reverb.level 0.7"
+		self.send "set synth.chorus.level 1.5"
+		self.send "set synth.chorus.depth 64.0"
+	end
+
+
+	### Issue a command to the synth, after possible logging.
+	###
+	def send( cmd )
+		self.log.debug( cmd )
+		self.socket.puts( cmd )
+	end
+end
+
+
diff --git a/theremin/lib/gpio.rb b/theremin/lib/gpio.rb
new file mode 100755
index 0000000..95cca86
--- /dev/null
+++ b/theremin/lib/gpio.rb
@@ -0,0 +1,121 @@
+# -*- ruby -*-
+# vim: set noet sta sw=4 ts=4 :
+
+require 'socket'
+require 'configurability'
+require 'loggability'
+require 'pathname'
+
+
+# A representation of a GPIO pin.
+# Manages basic reads/writes (HIGH/LOW).
+#
+class GPIO
+	extend Configurability,
+		Loggability
+
+	# Default read timeout.
+    TIMEOUT = 0.5
+
+	# The sysfs path.
+    BASE = Pathname( "/sys/class/gpio" )
+
+
+    # Loggability API
+    log_as :gpio
+
+
+	### Instance a new GPIO at +pin+.  It will be automatically exported.
+	###
+	def initialize( pin )
+		@pin = pin
+		@paths = {
+			export:    BASE + "export",
+			unexport:  BASE + "unexport",
+			edge:      BASE + "gpio#{pin}" + "edge",
+			direction: BASE + "gpio#{pin}" + "direction",
+			value:     BASE + "gpio#{pin}" + "value"
+		}
+
+		self.export rescue Errno::EBUSY nil
+	end
+
+	# The GPIO PIN number.
+	attr_reader :pin
+
+
+	### Mark this pin as either input or output.
+	###
+	def mode( dir )
+		case dir.to_sym
+		when :in, :out
+			self.set( :direction ) { dir.to_s }
+		else
+			raise "Mode must be :in or :out."
+		end
+	end
+
+
+	### Hint at voltage measurement capture.
+	###
+	def edge( mode )
+		case mode.to_sym
+		when :none, :rising, :falling, :both
+			self.set( :edge ) { mode.to_s }
+		else
+			raise "Edge must be one of: :none, :rising, :falling, or :both"
+		end
+	end
+
+
+	### Tell the operating system to make this gpio available to sysfs.
+	###
+	def export
+		self.set( :export ) { self.pin }
+	end
+
+
+	### Remove this gpio from sysfs.
+	###
+	def unexport
+		self.set( :unexport ) { self.pin }
+	end
+
+
+	### Write a single +val+ to the GPIO.
+	###
+	def write( val )
+		self.set( :value ) { val }
+	end
+
+
+	### Read a single value from the GPIO, with an optional timeout.
+	###
+	def read( timeout=TIMEOUT )
+		io = @paths[ :value ].open
+
+		ready = IO.select( [io], nil, nil, timeout )
+		return unless ready # timeout
+
+		rv = io.read( 1 ).to_i
+		self.log.debug "Read %p from GPIO %d" % [ rv, self.pin ]
+		return rv
+	ensure
+		io.close
+	end
+
+
+	#########
+	protected
+	#########
+
+	### Generic write helper.
+	###
+	def set( path, &block )
+		@paths[ path ].open( 'w' ) do |f|
+			self.log.debug "Writing %p to %p of GPIO %d" % [ block.yield, path, self.pin ]
+			f.puts( block.yield )
+		end
+	end
+end
+
diff --git a/theremin/lib/theremin.rb b/theremin/lib/theremin.rb
new file mode 100755
index 0000000..70fb766
--- /dev/null
+++ b/theremin/lib/theremin.rb
@@ -0,0 +1,293 @@
+# -*- ruby -*-
+# vim: set noet sta sw=4 ts=4 :
+
+require 'forwardable'
+require 'configurability'
+require 'loggability'
+require 'gpio'
+require 'fluidsynth'
+
+
+# A class that coordinates GPIO events and translates
+# them into commands for Fluidsynth.
+#
+class Theremin
+	extend Configurability,
+		Loggability,
+		Forwardable
+
+	# The speed of sound, in centmeters/sec.
+    SONICSPEED = 34300
+
+	# Loggability API
+	log_as :theremin
+
+	# Configuration API
+	#
+	configurability( :theremin ) do
+
+		##
+		# The host that fluidsynth lives at.
+		setting :host, default: 'localhost'
+
+		##
+		# The port that fluidsynth lives at.
+		setting :port, default: 9800
+
+		##
+		# The GPIO pin the pitch trigger is on.
+		setting :pitch_trigger do |val|
+			GPIO.new( val ) if val
+		end
+
+ 		##
+ 		# The GPIO pin the pitch echo measurement is on.
+ 		setting :pitch_echo do |val|
+ 			GPIO.new( val ) if val
+ 		end
+ 
+ 		##
+ 		# The GPIO pin the velocity trigger is on.
+ 		setting :velocity_trigger do |val|
+ 			GPIO.new( val ) if val
+ 		end
+ 
+ 		##
+ 		# The GPIO pin the velocity echo measurement is on.
+ 		setting :velocity_echo do |val|
+ 			GPIO.new( val ) if val
+ 		end
+
+		##
+		# The soundfont to use for the synth.  Will look in the
+		# current working directory by default, but absolute paths 
+		# can be used for system sounds.
+		setting :font, default: 'Theremin.sf2' do |val|
+			val = Pathname( val )
+			val = Pathname.pwd + val unless val.absolute?
+			val
+		end
+
+
+		##
+		# If a note is "stuck", turn if off after this many seconds.
+		setting :cancel_after, default: 5
+
+		##
+		# A reasonable distance in feet for the theremin to map notes.
+		setting :distance_max, default: 4
+
+		##
+		# Initial synth volume.
+		setting :gain, default: 1.0
+
+		##
+		# Enable reverb?
+		setting :reverb, default: true
+
+		##
+		# Enable chorus?
+		setting :chorus, default: true
+
+		##
+		# What instrument to use from the loaded SF2.
+		setting :instrument_index, default: 1
+
+		##
+		# Portamento.  Value in milliseconds to glide between notes to
+		# emulate analog theremin.  0 disables completely.  Values
+		# are in 128ms increments.
+		setting :glide, default: 768 do |val|
+			val = 128 if val < 128 && ! val.zero?
+			val = ( val.to_f / 128 ).round
+			val
+		end
+
+		##
+		# How frequently should the range finders measure distance?
+		# Value in seconds.
+		setting :sample_interval, default: 0.3
+
+		##
+		# Only change the note if the range finder value moves +/- this much
+		# between samples.  This helps hold pitch, and avoids "warbles".
+		setting :slew, default: 5
+	end
+
+
+	### Instance a new Theremin daemon.
+	###
+	def initialize
+		# TODO: @pins = %i[ pitch_trigger pitch_echo velocity_trigger velocity_echo ]
+		@pins = %i[ pitch_trigger ]
+
+		self.setup_gpio
+
+		@timeout = 0
+		@synth   = FluidSynth.new( self.class.host, self.class.port )
+		@running = false
+		@threads = []
+
+	rescue => err
+		self.log.warn( err.message )
+		self.stop rescue nil
+    end
+
+	# Delegate various methods directly to the underlying synth instance.
+    def_delegators :@synth, :gain, :glide, :load, :reverb, :chorus, :instrument
+
+	# The names of the GPIO pins.
+	attr_reader :pins
+
+	# The Fluidsynth instance.
+    attr_reader :synth
+
+	# Is this Theremin currently running?
+    attr_reader :running
+
+
+	### Start polling the GPIO for measurements.
+	###
+	def start
+		@running = true
+		self.synth.connect
+
+		self.gain( self.class.gain )
+		self.glide( self.class.glide )
+		self.load( self.class.font.to_s )
+		self.reverb( self.class.reverb )
+		self.chorus( self.class.chorus )
+		self.instrument( self.class.instrument_index )
+
+		@threads << self.note_thread
+		self.log.warn "Waiting for interaction, or ctrl-c to exit."
+		@threads.map( &:join )
+	end
+
+
+	### Cleanly shutdown GPIO and synth.
+	###
+	def stop
+		@running = false
+		self.pins.each {|pin| self.class.send( pin ).unexport rescue nil }
+		self.synth.socket.close
+	end
+
+    
+    #########
+    protected
+    #########
+
+	### Measure pitch distance, and manage notes sent to the synth.
+	###
+	def note_thread
+		self.log.info "Starting note/pitch measurements (every %s/sec) within %d feet." % [
+			self.class.sample_interval,
+			self.class.distance_max
+		]
+
+		return self.running_thread do
+			distance = self.distance
+			note = self.distance_to_note( distance )
+
+			# Only play if within maximum distance.
+			#
+			if distance <= self.class.distance_max
+				self.log.debug "Pitch distance %0.2f (note %s)" % [ distance, note ]
+
+				# Hold the note if it is unchanged within slew amount.
+				#
+				if synth.lastnote
+					if note <= synth.lastnote - self.class.slew || note >= synth.lastnote + self.class.slew
+						synth.playnote( note )
+					end
+				else
+					synth.playnote( note )
+				end
+
+			# Cancel note if timeout is hit.
+			#
+			elsif @timeout >= self.class.cancel_after
+				@timeout = 0
+				synth.stopnote
+			end
+
+			sleep self.class.sample_interval
+			@timeout += self.class.sample_interval
+		end
+	end
+
+
+	### Create a new thread loop that returns when @running is false.
+	###
+	def running_thread( &block )
+		return Thread.new do
+			while @running
+				yield
+			end
+		end
+	end
+
+
+	### Validate GPIO config, and mark edge behavior for the echo measurement pins.
+	###
+	def setup_gpio
+		pincheck = self.pins.map{|p| self.class.send(p) }
+
+		if pincheck.any?( nil )
+			self.stop rescue nil
+			raise "GPIO pins are required configuration options: %p" % [ self.pins ]
+		end
+
+		self.class.pitch_trigger.edge( :both )
+		# self.class.pitch_echo.edge( :both )
+		# TODO: self.class.velocity_echo.edge( :both )
+	end
+
+
+	### For a given +distance+ in feet, convert into a valid MIDI note
+	### within the range.
+	###
+	def distance_to_note( distance )
+		midi_start   = 107 # 127, but the theramin soundfont maxes out at 107.
+		midi_end     = 0
+		distance_min = 0
+
+		slope = 1.0 * ( midi_end - midi_start ) / ( self.class.distance_max - distance_min )
+		return midi_start + ( slope * ( distance - distance_min ) ).round
+	end
+
+
+	### TODO: make generic for a trigger/echo pin pair
+	### Returns detected distance in feet.
+	###
+	def distance
+		self.class.pitch_trigger.mode( :out )
+		self.class.pitch_trigger.write( 1 )
+		sleep 0.00001
+		self.class.pitch_trigger.write( 0 )
+		self.class.pitch_trigger.mode( :in )
+
+		duration = Time.now
+		while self.class.pitch_trigger.read == 0
+			starttime = Time.now
+			break if starttime - duration > GPIO::TIMEOUT
+		end
+		while self.class.pitch_trigger.read == 1
+			stoptime = Time.now
+			break if stoptime - duration > GPIO::TIMEOUT
+		end
+
+		elapsed = stoptime - starttime
+		distance = ( elapsed * SONICSPEED ) / 2
+		distance = 0 if distance < 0
+
+		distance = distance / 30.48
+
+		return distance
+
+	rescue
+		return 0
+	end
+end
+
diff --git a/theremin/run b/theremin/run
new file mode 100755
index 0000000..6598790
--- /dev/null
+++ b/theremin/run
@@ -0,0 +1,19 @@
+#!/usr/bin/env ruby
+# vim: set noet sta sw=4 ts=4 :
+
+$LOAD_PATH << './lib'
+require 'pathname'
+require 'configurability'
+require 'theremin'
+
+Configurability::Config.load( 'config.yml' ).install
+
+theremin = Theremin.new
+
+Signal.trap( "INT" ) do
+	puts "\n\nShutting down..."
+	theremin.stop if theremin.running
+end
+
+theremin.start
+