commit e75063a0f3cd0e3f64edb0305c792c837b2b2e11
Author: Lukas <lukas.schwarz@posteo.de>
Date:   Mon Jul 5 10:50:11 2021 +0200

    Initial commit

diff --git a/amp_controller.pdf b/amp_controller.pdf
new file mode 100644
index 0000000..618ecce
Binary files /dev/null and b/amp_controller.pdf differ
diff --git a/amp_controller.py b/amp_controller.py
new file mode 100644
index 0000000..305d5f3
--- /dev/null
+++ b/amp_controller.py
@@ -0,0 +1,133 @@
+#!/usr/bin/env python3
+
+import RPi.GPIO as gpio
+import time
+import logging
+import re
+import subprocess
+
+
+class amp_controller:
+    """Amp controller class to hold certain attributes and methods for automatically
+    turning on and off the amplifier.
+    """
+
+    SHUTOFF_TIMER_DURATION = 5 * 60  # in seconds
+    SHORT_TIMER_DURATION = 60
+    CHECK_FREQUENCY = 1  # in seconds
+    MPD_LOG_FILE = "/var/log/mpd/mpd.log"
+    PULSE_CARD_PATH = "/proc/asound/card0/pcm0p/sub0/status"
+    GPIO_PINS = {"Relay": 2, "Phono": 4, "Tape": 14, "CD": 15}
+
+    powered = False
+    last_mpd_output = ""
+
+    gpio.setmode(gpio.BCM)
+    logging.basicConfig(level=logging.DEBUG)
+
+    def setup_pins(self) -> None:
+        """Set all GPIO pins to output."""
+        for pin in self.GPIO_PINS.values():
+            gpio.setup(pin, gpio.OUT)
+
+    def set_channel(self, channel_name) -> None:
+        """Set the channel on the amplifier."""
+        pin = self.GPIO_PINS[channel_name]
+        gpio.output(pin, True)
+        time.sleep(0.5)
+        gpio.output(pin, False)
+
+    def power(self, state) -> None:
+        """Turn the amplifier on or off via the GPIO pins."""
+        if state == "on":
+            gpio.output(self.GPIO_PINS["Relay"], True)
+            time.sleep(0.5)
+            self.powered = True
+        else:
+            gpio.output(self.GPIO_PINS["Relay"], False)
+            self.powered = False
+
+    def pulse_playing(self) -> bool:
+        """Return True if there is something playing on the specified Pulseaudio card.
+        Return False in every other case.
+        """
+        output = subprocess.check_output(
+            "cat " + self.PULSE_CARD_PATH, shell=True, universal_newlines=True
+        )
+
+        state = output.split("\n")[0]
+
+        if "RUNNING" in state:
+            logging.debug("Pulseaudio connected")
+            return True
+
+        return False
+
+    def mpd_client_connected(self) -> bool:
+        """Return True if an mpd client is connected and False if not.
+        Requires 'log_level="secure"' or "debug" to be set in mpd.conf.
+        """
+        output = subprocess.check_output(
+            ["tail", "-1", self.MPD_LOG_FILE], universal_newlines=True
+        )
+
+        if output != self.last_mpd_output:
+            self.last_mpd_output = output
+            if re.match(".* opened from .*", output):
+                logging.debug("mpd client connected")
+                return True
+
+        return False
+
+
+if __name__ == "__main__":
+    ac = amp_controller()
+    ac.setup_pins()
+    ac.power("on")
+    ac.set_channel("CD")
+
+    timer = ac.SHUTOFF_TIMER_DURATION
+    while True:
+        # Check for changes every second.
+        time.sleep(ac.CHECK_FREQUENCY)
+
+        # Only connected, nothing playing.
+        if ac.mpd_client_connected():
+            if not ac.powered:
+                ac.power("on")
+                ac.set_channel("CD")
+
+            # (Re)set the timer to the short duration if a client connects. Don't
+            # overwrite a running timer currently greater than the short duration one.
+            if timer > 0 and timer <= ac.SHORT_TIMER_DURATION:
+                timer = ac.SHORT_TIMER_DURATION
+            elif timer < 0:
+                timer = ac.SHORT_TIMER_DURATION
+
+            logging.debug("Timer set to {}".format(timer))
+
+        if timer == 0:
+            logging.debug("Timer ran out")
+            ac.power("off")
+
+        if ac.pulse_playing() and not ac.powered:
+            ac.power("on")
+            ac.set_channel("CD")
+
+            # Reset the timer.
+            timer = ac.SHUTOFF_TIMER_DURATION
+
+        # Start the counter if nothing is currently playing.
+        if not ac.pulse_playing():
+            timer -= ac.CHECK_FREQUENCY
+            logging.debug("Nothing playing.")
+            logging.debug("Timer: " + str(timer))
+            continue
+
+            if timer < -1000:  # Just to be safe and avoid weird overflows.
+                timer = -1
+
+        # If there is something playing (no ifs matched) just reset the counter.
+        timer = ac.SHUTOFF_TIMER_DURATION
+        logging.debug("Something is playing.")
+        logging.debug("Timer: " + str(timer))
diff --git a/amp_controller.sch b/amp_controller.sch
new file mode 100644
index 0000000..1db8e8c
--- /dev/null
+++ b/amp_controller.sch
@@ -0,0 +1,378 @@
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