Adding mixer example

Adding mixer volume example for the Feather RP2040 Prop-Maker guide

RP2040_Prop-Maker_Feather_Examples/CircuitPython_Mixer_Volume_Example/code.py

@@ -0,0 +1,46 @@
+# SPDX-FileCopyrightText: 2023 ladyada for Adafruit Industries
+#
+# SPDX-License-Identifier: MIT
+
+import audiobusio
+import audiocore
+import board
+import digitalio
+import keypad
+import analogio
+import audiomixer
+
+SOUND_FILE = "StreetChicken.wav"
+
+power = digitalio.DigitalInOut(board.EXTERNAL_POWER)
+power.switch_to_output(value=True)
+
+analog_pin = analogio.AnalogIn(board.A0)
+
+keys = keypad.Keys((board.BUTTON,), value_when_pressed=False)
+
+i2s = audiobusio.I2SOut(board.I2S_BIT_CLOCK, board.I2S_WORD_SELECT, board.I2S_DATA)
+music = audiocore.WaveFile(SOUND_FILE)
+mixer = audiomixer.Mixer(voice_count=1, sample_rate=music.sample_rate, channel_count=1,
+                         bits_per_sample=music.bits_per_sample, samples_signed=True)
+i2s.play(mixer)
+
+sound = False
+last_pot = 0
+
+while True:
+    if abs(last_pot - analog_pin.value) > 1000:
+        last_pot = analog_pin.value
+        volume = 1.0 - last_pot / 65535
+        print(volume)
+        mixer.voice[0].level = volume
+
+    if sound and not mixer.voice[0].playing:
+        print("Playing now!")
+        mixer.voice[0].play(music)
+
+    event = keys.events.get()
+    if event and event.pressed:
+        print("click")
+        sound = not sound
+        mixer.voice[0].stop()