savetheclocktower · October 6, 2024 20:19 · savetheclocktower · Feb 3, 2021 · virginiebjt · Feb 8, 2021
diff --git a/README.md b/README.md
diff --git a/monitor-volume b/monitor-volume
 #!/usr/bin/env python3

 """
 The daemon responsible for changing the volume in response to a turn or press
 of the volume knob.

 The volume knob is a rotary encoder. It turns infinitely in either direction.
 Turning it to the right will increase the volume; turning it to the left will
 decrease the volume. The knob can also be pressed like a button in order to
 turn muting on or off.

 The knob uses two GPIO pins and we need some extra logic to decode it. The
 button we can just treat like an ordinary button. Rather than poll
 constantly, we use threads and interrupts to listen on all three pins in one
 script.
 """

 import os
 import signal
 import subprocess
 import sys
 import threading

 from RPi import GPIO
 from queue import Queue

 DEBUG = False

 # SETTINGS
 # ========

 # The two pins that the encoder uses (BCM numbering).
 GPIO_A = 26   
 GPIO_B = 19

 # The pin that the knob's button is hooked up to. If you have no button, set
 # this to None.
 GPIO_BUTTON = 13 

 # The minimum and maximum volumes, as percentages.
 #
 # The default max is less than 100 to prevent distortion. The default min is
 # greater than zero because if your system is like mine, sound gets
 # completely inaudible _long_ before 0%. If you've got a hardware amp or
 # serious speakers or something, your results will vary.
 VOLUME_MIN = 60
 VOLUME_MAX = 96

 # The amount you want one click of the knob to increase or decrease the
 # volume. I don't think that non-integer values work here, but you're welcome
 # to try.
 VOLUME_INCREMENT = 1

 # (END SETTINGS)
 # 


 # When the knob is turned, the callback happens in a separate thread. If
 # those turn callbacks fire erratically or out of order, we'll get confused
 # about which direction the knob is being turned, so we'll use a queue to
 # enforce FIFO. The callback will push onto a queue, and all the actual
 # volume-changing will happen in the main thread.
 QUEUE = Queue()

 # When we put something in the queue, we'll use an event to signal to the
 # main thread that there's something in there. Then the main thread will
 # process the queue and reset the event. If the knob is turned very quickly,
 # this event loop will fall behind, but that's OK because it consumes the
 # queue completely each time through the loop, so it's guaranteed to catch up.
 EVENT = threading.Event()

 def debug(str):
  if not DEBUG:
    return
  print(str)

 class RotaryEncoder:
  """
  A class to decode mechanical rotary encoder pulses.

  Ported to RPi.GPIO from the pigpio sample here: 
  http://abyz.co.uk/rpi/pigpio/examples.html
  """
  
  def __init__(self, gpioA, gpioB, callback=None, buttonPin=None, buttonCallback=None):
    """
    Instantiate the class. Takes three arguments: the two pin numbers to
    which the rotary encoder is connected, plus a callback to run when the
    switch is turned.
    
    The callback receives one argument: a `delta` that will be either 1 or -1.
    One of them means that the dial is being turned to the right; the other
    means that the dial is being turned to the left. I'll be damned if I know
    yet which one is which.
    """
    
    self.lastGpio = None
    self.gpioA    = gpioA
    self.gpioB    = gpioB
    self.callback = callback
    
    self.gpioButton     = buttonPin
    self.buttonCallback = buttonCallback
    
    self.levA = 0
    self.levB = 0
    
    GPIO.setmode(GPIO.BCM)
    GPIO.setup(self.gpioA, GPIO.IN, pull_up_down=GPIO.PUD_UP)
    GPIO.setup(self.gpioB, GPIO.IN, pull_up_down=GPIO.PUD_UP)
    
    GPIO.add_event_detect(self.gpioA, GPIO.BOTH, self._callback)
    GPIO.add_event_detect(self.gpioB, GPIO.BOTH, self._callback)
    
    if self.gpioButton:
      GPIO.setup(self.gpioButton, GPIO.IN, pull_up_down=GPIO.PUD_UP)
      GPIO.add_event_detect(self.gpioButton, GPIO.FALLING, self._buttonCallback, bouncetime=500)
    
    
  def destroy(self):
    GPIO.remove_event_detect(self.gpioA)
    GPIO.remove_event_detect(self.gpioB)
    GPIO.cleanup()
    
  def _buttonCallback(self, channel):
    self.buttonCallback(GPIO.input(channel))
    
  def _callback(self, channel):
    level = GPIO.input(channel)
    if channel == self.gpioA:
      self.levA = level
    else:
      self.levB = level
      
    # Debounce.
    if channel == self.lastGpio:
      return
    
    # When both inputs are at 1, we'll fire a callback. If A was the most
    # recent pin set high, it'll be forward, and if B was the most recent pin
    # set high, it'll be reverse.
    self.lastGpio = channel
    if channel == self.gpioA and level == 1:
      if self.levB == 1:
        self.callback(1)
    elif channel == self.gpioB and level == 1:
      if self.levA == 1:
        self.callback(-1)

 class VolumeError(Exception):
  pass

 class Volume:
  """
  A wrapper API for interacting with the volume settings on the RPi.
  """
  MIN = VOLUME_MIN
  MAX = VOLUME_MAX
  INCREMENT = VOLUME_INCREMENT
  
  def __init__(self):
    # Set an initial value for last_volume in case we're muted when we start.
    self.last_volume = self.MIN
    self._sync()
  
  def up(self):
    """
    Increases the volume by one increment.
    """
    return self.change(self.INCREMENT)
    
  def down(self):
    """
    Decreases the volume by one increment.
    """
    return self.change(-self.INCREMENT)
    
  def change(self, delta):
    v = self.volume + delta
    v = self._constrain(v)
    return self.set_volume(v)
  
  def set_volume(self, v):
    """
    Sets volume to a specific value.
    """
    self.volume = self._constrain(v)
    output = self.amixer("set 'PCM' unmute {}%".format(v))
    self._sync(output)
    return self.volume
    
  def toggle(self):
    """
    Toggles muting between on and off.
    """
    if self.is_muted:
      output = self.amixer("set 'PCM' unmute")
    else:
      # We're about to mute ourselves, so we should remember the last volume
      # value we had because we'll want to restore it later.
      self.last_volume = self.volume
      output = self.amixer("set 'PCM' mute")
  
    self._sync(output)
    if not self.is_muted:
      # If we just unmuted ourselves, we should restore whatever volume we
      # had previously.
      self.set_volume(self.last_volume)
    return self.is_muted
  
  def status(self):
    if self.is_muted:
      return "{}% (muted)".format(self.volume)
    return "{}%".format(self.volume)
  
  # Read the output of `amixer` to get the system volume and mute state.
  #
  # This is designed not to do much work because it'll get called with every
  # click of the knob in either direction, which is why we're doing simple
  # string scanning and not regular expressions.
  def _sync(self, output=None):
    if output is None:
      output = self.amixer("get 'PCM'")
      
    lines = output.readlines()
    if DEBUG:
      strings = [line.decode('utf8') for line in lines]
      debug("OUTPUT:")
      debug("".join(strings))
    last = lines[-1].decode('utf-8')
    
    # The last line of output will have two values in square brackets. The
    # first will be the volume (e.g., "[95%]") and the second will be the
    # mute state ("[off]" or "[on]").
    i1 = last.rindex('[') + 1
    i2 = last.rindex(']')

    self.is_muted = last[i1:i2] == 'off'
    
    i1 = last.index('[') + 1
    i2 = last.index('%')
    # In between these two will be the percentage value.
    pct = last[i1:i2]

    self.volume = int(pct)
  
  # Ensures the volume value is between our minimum and maximum.
  def _constrain(self, v):
    if v < self.MIN:
      return self.MIN
    if v > self.MAX:
      return self.MAX
    return v
    
  def amixer(self, cmd):
    p = subprocess.Popen("amixer {}".format(cmd), shell=True, stdout=subprocess.PIPE)
    code = p.wait()
    if code != 0:
      raise VolumeError("Unknown error")
      sys.exit(0)
    
    return p.stdout


 if __name__ == "__main__":
  
  gpioA = GPIO_A
  gpioB = GPIO_B
  gpioButton = GPIO_BUTTON
  
  v = Volume()
  
  def on_press(value):
    v.toggle()
    print("Toggled mute to: {}".format(v.is_muted))
    EVENT.set()
  
  # This callback runs in the background thread. All it does is put turn
  # events into a queue and flag the main thread to process them. The
  # queueing ensures that we won't miss anything if the knob is turned
  # extremely quickly.
  def on_turn(delta):
    QUEUE.put(delta)
    EVENT.set()
    
  def consume_queue():
    while not QUEUE.empty():
      delta = QUEUE.get()
      handle_delta(delta)
  
  def handle_delta(delta):
    if v.is_muted:
      debug("Unmuting")
      v.toggle()
    if delta == 1:
      vol = v.up()
    else:
      vol = v.down()
    print("Set volume to: {}".format(vol))
    
  def on_exit(a, b):
    print("Exiting...")
    encoder.destroy()
    sys.exit(0)
    
  debug("Volume knob using pins {} and {}".format(gpioA, gpioB))
  
  if gpioButton != None:
    debug("Volume button using pin {}".format(gpioButton))
  
  debug("Initial volume: {}".format(v.volume))

  encoder = RotaryEncoder(GPIO_A, GPIO_B, callback=on_turn, buttonPin=GPIO_BUTTON, buttonCallback=on_press)
  signal.signal(signal.SIGINT, on_exit)
  
  while True:
    # This is the best way I could come up with to ensure that this script
    # runs indefinitely without wasting CPU by polling. The main thread will
    # block quietly while waiting for the event to get flagged. When the knob
    # is turned we're able to respond immediately, but when it's not being
    # turned we're not looping at all.
    # 
    # The 1200-second (20 minute) timeout is a hack; for some reason, if I
    # don't specify a timeout, I'm unable to get the SIGINT handler above to
    # work properly. But if there is a timeout set, even if it's a very long
    # timeout, then Ctrl-C works as intended. No idea why.
    EVENT.wait(1200)
    consume_queue()
    EVENT.clear()
diff --git a/monitor-volume.service b/monitor-volume.service
 [Unit]
 Description=Volume knob monitor

 [Service]
 User=pi
 Group=pi
 ExecStart=/home/pi/bin/monitor-volume

 [Install]
 WantedBy=multi-user.target
Description	BCM #	Board #
knob A	GPIO 26	37
knob B	GPIO 19	35
knob ground	ground pin below GPIO 26	39
button common	GPIO 13	33
button ground	ground pin opposite GPIO 13	34
	#!/usr/bin/env python3

	"""
	The daemon responsible for changing the volume in response to a turn or press
	of the volume knob.

	The volume knob is a rotary encoder. It turns infinitely in either direction.
	Turning it to the right will increase the volume; turning it to the left will
	decrease the volume. The knob can also be pressed like a button in order to
	turn muting on or off.

	The knob uses two GPIO pins and we need some extra logic to decode it. The
	button we can just treat like an ordinary button. Rather than poll
	constantly, we use threads and interrupts to listen on all three pins in one
	script.
	"""

	import os
	import signal
	import subprocess
	import sys
	import threading

	from RPi import GPIO
	from queue import Queue

	DEBUG = False

	# SETTINGS
	# ========

	# The two pins that the encoder uses (BCM numbering).
	GPIO_A = 26
	GPIO_B = 19

	# The pin that the knob's button is hooked up to. If you have no button, set
	# this to None.
	GPIO_BUTTON = 13

	# The minimum and maximum volumes, as percentages.
	#
	# The default max is less than 100 to prevent distortion. The default min is
	# greater than zero because if your system is like mine, sound gets
	# completely inaudible _long_ before 0%. If you've got a hardware amp or
	# serious speakers or something, your results will vary.
	VOLUME_MIN = 60
	VOLUME_MAX = 96

	# The amount you want one click of the knob to increase or decrease the
	# volume. I don't think that non-integer values work here, but you're welcome
	# to try.
	VOLUME_INCREMENT = 1

	# (END SETTINGS)
	#


	# When the knob is turned, the callback happens in a separate thread. If
	# those turn callbacks fire erratically or out of order, we'll get confused
	# about which direction the knob is being turned, so we'll use a queue to
	# enforce FIFO. The callback will push onto a queue, and all the actual
	# volume-changing will happen in the main thread.
	QUEUE = Queue()

	# When we put something in the queue, we'll use an event to signal to the
	# main thread that there's something in there. Then the main thread will
	# process the queue and reset the event. If the knob is turned very quickly,
	# this event loop will fall behind, but that's OK because it consumes the
	# queue completely each time through the loop, so it's guaranteed to catch up.
	EVENT = threading.Event()

	def debug(str):
	if not DEBUG:
	return
	print(str)

	class RotaryEncoder:
	"""
	A class to decode mechanical rotary encoder pulses.

	Ported to RPi.GPIO from the pigpio sample here:
	http://abyz.co.uk/rpi/pigpio/examples.html
	"""

	def __init__(self, gpioA, gpioB, callback=None, buttonPin=None, buttonCallback=None):
	"""
	Instantiate the class. Takes three arguments: the two pin numbers to
	which the rotary encoder is connected, plus a callback to run when the
	switch is turned.

	The callback receives one argument: a `delta` that will be either 1 or -1.
	One of them means that the dial is being turned to the right; the other
	means that the dial is being turned to the left. I'll be damned if I know
	yet which one is which.
	"""

	self.lastGpio = None
	self.gpioA = gpioA
	self.gpioB = gpioB
	self.callback = callback

	self.gpioButton = buttonPin
	self.buttonCallback = buttonCallback

	self.levA = 0
	self.levB = 0

	GPIO.setmode(GPIO.BCM)
	GPIO.setup(self.gpioA, GPIO.IN, pull_up_down=GPIO.PUD_UP)
	GPIO.setup(self.gpioB, GPIO.IN, pull_up_down=GPIO.PUD_UP)

	GPIO.add_event_detect(self.gpioA, GPIO.BOTH, self._callback)
	GPIO.add_event_detect(self.gpioB, GPIO.BOTH, self._callback)

	if self.gpioButton:
	GPIO.setup(self.gpioButton, GPIO.IN, pull_up_down=GPIO.PUD_UP)
	GPIO.add_event_detect(self.gpioButton, GPIO.FALLING, self._buttonCallback, bouncetime=500)


	def destroy(self):
	GPIO.remove_event_detect(self.gpioA)
	GPIO.remove_event_detect(self.gpioB)
	GPIO.cleanup()

	def _buttonCallback(self, channel):
	self.buttonCallback(GPIO.input(channel))

	def _callback(self, channel):
	level = GPIO.input(channel)
	if channel == self.gpioA:
	self.levA = level
	else:
	self.levB = level

	# Debounce.
	if channel == self.lastGpio:
	return

	# When both inputs are at 1, we'll fire a callback. If A was the most
	# recent pin set high, it'll be forward, and if B was the most recent pin
	# set high, it'll be reverse.
	self.lastGpio = channel
	if channel == self.gpioA and level == 1:
	if self.levB == 1:
	self.callback(1)
	elif channel == self.gpioB and level == 1:
	if self.levA == 1:
	self.callback(-1)

	class VolumeError(Exception):
	pass

	class Volume:
	"""
	A wrapper API for interacting with the volume settings on the RPi.
	"""
	MIN = VOLUME_MIN
	MAX = VOLUME_MAX
	INCREMENT = VOLUME_INCREMENT

	def __init__(self):
	# Set an initial value for last_volume in case we're muted when we start.
	self.last_volume = self.MIN
	self._sync()

	def up(self):
	"""
	Increases the volume by one increment.
	"""
	return self.change(self.INCREMENT)

	def down(self):
	"""
	Decreases the volume by one increment.
	"""
	return self.change(-self.INCREMENT)

	def change(self, delta):
	v = self.volume + delta
	v = self._constrain(v)
	return self.set_volume(v)

	def set_volume(self, v):
	"""
	Sets volume to a specific value.
	"""
	self.volume = self._constrain(v)
	output = self.amixer("set 'PCM' unmute {}%".format(v))
	self._sync(output)
	return self.volume

	def toggle(self):
	"""
	Toggles muting between on and off.
	"""
	if self.is_muted:
	output = self.amixer("set 'PCM' unmute")
	else:
	# We're about to mute ourselves, so we should remember the last volume
	# value we had because we'll want to restore it later.
	self.last_volume = self.volume
	output = self.amixer("set 'PCM' mute")

	self._sync(output)
	if not self.is_muted:
	# If we just unmuted ourselves, we should restore whatever volume we
	# had previously.
	self.set_volume(self.last_volume)
	return self.is_muted

	def status(self):
	if self.is_muted:
	return "{}% (muted)".format(self.volume)
	return "{}%".format(self.volume)

	# Read the output of `amixer` to get the system volume and mute state.
	#
	# This is designed not to do much work because it'll get called with every
	# click of the knob in either direction, which is why we're doing simple
	# string scanning and not regular expressions.
	def _sync(self, output=None):
	if output is None:
	output = self.amixer("get 'PCM'")

	lines = output.readlines()
	if DEBUG:
	strings = [line.decode('utf8') for line in lines]
	debug("OUTPUT:")
	debug("".join(strings))
	last = lines[-1].decode('utf-8')

	# The last line of output will have two values in square brackets. The
	# first will be the volume (e.g., "[95%]") and the second will be the
	# mute state ("[off]" or "[on]").
	i1 = last.rindex('[') + 1
	i2 = last.rindex(']')

	self.is_muted = last[i1:i2] == 'off'

	i1 = last.index('[') + 1
	i2 = last.index('%')
	# In between these two will be the percentage value.
	pct = last[i1:i2]

	self.volume = int(pct)

	# Ensures the volume value is between our minimum and maximum.
	def _constrain(self, v):
	if v < self.MIN:
	return self.MIN
	if v > self.MAX:
	return self.MAX
	return v

	def amixer(self, cmd):
	p = subprocess.Popen("amixer {}".format(cmd), shell=True, stdout=subprocess.PIPE)
	code = p.wait()
	if code != 0:
	raise VolumeError("Unknown error")
	sys.exit(0)

	return p.stdout


	if __name__ == "__main__":

	gpioA = GPIO_A
	gpioB = GPIO_B
	gpioButton = GPIO_BUTTON

	v = Volume()

	def on_press(value):
	v.toggle()
	print("Toggled mute to: {}".format(v.is_muted))
	EVENT.set()

	# This callback runs in the background thread. All it does is put turn
	# events into a queue and flag the main thread to process them. The
	# queueing ensures that we won't miss anything if the knob is turned
	# extremely quickly.
	def on_turn(delta):
	QUEUE.put(delta)
	EVENT.set()

	def consume_queue():
	while not QUEUE.empty():
	delta = QUEUE.get()
	handle_delta(delta)

	def handle_delta(delta):
	if v.is_muted:
	debug("Unmuting")
	v.toggle()
	if delta == 1:
	vol = v.up()
	else:
	vol = v.down()
	print("Set volume to: {}".format(vol))

	def on_exit(a, b):
	print("Exiting...")
	encoder.destroy()
	sys.exit(0)

	debug("Volume knob using pins {} and {}".format(gpioA, gpioB))

	if gpioButton != None:
	debug("Volume button using pin {}".format(gpioButton))

	debug("Initial volume: {}".format(v.volume))

	encoder = RotaryEncoder(GPIO_A, GPIO_B, callback=on_turn, buttonPin=GPIO_BUTTON, buttonCallback=on_press)
	signal.signal(signal.SIGINT, on_exit)

	while True:
	# This is the best way I could come up with to ensure that this script
	# runs indefinitely without wasting CPU by polling. The main thread will
	# block quietly while waiting for the event to get flagged. When the knob
	# is turned we're able to respond immediately, but when it's not being
	# turned we're not looping at all.
	#
	# The 1200-second (20 minute) timeout is a hack; for some reason, if I
	# don't specify a timeout, I'm unable to get the SIGINT handler above to
	# work properly. But if there is a timeout set, even if it's a very long
	# timeout, then Ctrl-C works as intended. No idea why.
	EVENT.wait(1200)
	consume_queue()
	EVENT.clear()
	[Unit]
	Description=Volume knob monitor

	[Service]
	User=pi
	Group=pi
	ExecStart=/home/pi/bin/monitor-volume

	[Install]
	WantedBy=multi-user.target