audiopwmio – Audio output via digital PWM

The audiopwmio module contains classes to provide access to audio IO.

All classes change hardware state and should be deinitialized when they are no longer needed if the program continues after use. To do so, either call deinit() or use a context manager. See Lifetime and ContextManagers for more info.

Since CircuitPython 5, Mixer, RawSample and WaveFile are moved to audiocore.

class audiopwmio.PWMAudioOut(left_channel: microcontroller.Pin, *, right_channel: Optional[microcontroller.Pin] = None, quiescent_value: int = 32768)

Output an analog audio signal by varying the PWM duty cycle.

Create a PWMAudioOut object associated with the given pin(s). This allows you to play audio signals out on the given pin(s). In contrast to mod:audioio, the pin(s) specified are digital pins, and are driven with a device-dependent PWM signal.

Parameters:
  • left_channel (Pin) – The pin to output the left channel to
  • right_channel (Pin) – The pin to output the right channel to
  • quiescent_value (int) – The output value when no signal is present. Samples should start and end with this value to prevent audible popping.

Simple 8ksps 440 Hz sin wave:

import audiocore
import audiopwmio
import board
import array
import time
import math

# Generate one period of sine wav.
length = 8000 // 440
sine_wave = array.array("H", [0] * length)
for i in range(length):
    sine_wave[i] = int(math.sin(math.pi * 2 * i / length) * (2 ** 15) + 2 ** 15)

dac = audiopwmio.PWMAudioOut(board.SPEAKER)
sine_wave = audiocore.RawSample(sine_wave, sample_rate=8000)
dac.play(sine_wave, loop=True)
time.sleep(1)
dac.stop()

Playing a wave file from flash:

import board
import audiocore
import audiopwmio
import digitalio

# Required for CircuitPlayground Express
speaker_enable = digitalio.DigitalInOut(board.SPEAKER_ENABLE)
speaker_enable.switch_to_output(value=True)

data = open("cplay-5.1-16bit-16khz.wav", "rb")
wav = audiocore.WaveFile(data)
a = audiopwmio.PWMAudioOut(board.SPEAKER)

print("playing")
a.play(wav)
while a.playing:
  pass
print("stopped")
playing :bool

True when an audio sample is being output even if paused. (read-only)

paused :bool

True when playback is paused. (read-only)

deinit(self)

Deinitialises the PWMAudioOut and releases any hardware resources for reuse.

__enter__(self)

No-op used by Context Managers.

__exit__(self)

Automatically deinitializes the hardware when exiting a context. See Lifetime and ContextManagers for more info.

play(self, sample: _typing.AudioSample, *, loop: bool = False)

Plays the sample once when loop=False and continuously when loop=True. Does not block. Use playing to block.

Sample must be an audiocore.WaveFile, audiocore.RawSample, audiomixer.Mixer or audiomp3.MP3Decoder.

The sample itself should consist of 16 bit samples. Microcontrollers with a lower output resolution will use the highest order bits to output. For example, the SAMD21 has a 10 bit DAC that ignores the lowest 6 bits when playing 16 bit samples.

stop(self)

Stops playback and resets to the start of the sample.

pause(self)

Stops playback temporarily while remembering the position. Use resume to resume playback.

resume(self)

Resumes sample playback after pause().