Description
CircuitPython version
Adafruit CircuitPython 9.2.1 on 2024-11-20; Waveshare RP2040-Plus (16MB) with rp2040
Board ID:waveshare_rp2040_plus_16mbCode/REPL
import array
import time
import audiobusio
import board
import math
# Constants
SAMPLE_RATE = 22050 # Sample rate in Hz
DURATION = 0.4 # Recording duration in seconds
BUFFER_SIZE = int(SAMPLE_RATE * DURATION)
# Prepare a buffer to record into
buffer = array.array("H", [0] * BUFFER_SIZE)
with audiobusio.PDMIn(
board.GP2,
board.GP3,
sample_rate=SAMPLE_RATE,
mono=True,
oversample=64,
bit_depth=16,
startup_delay=0.2
) as mic:
# discard short period of data
dump_length = int(SAMPLE_RATE*0.01)
tmp_buffer = array.array("H", [0] * dump_length)
while(dump_length > 0):
samples_read = mic.record(tmp_buffer, len(tmp_buffer))
dump_length -= samples_read
print("Recording...")
offset = 0
while offset < len(buffer):
chunk_size = min(512, len(buffer) - offset)
samples_used = mic.record(memoryview(buffer)[offset:offset+chunk_size], chunk_size)
offset += samples_used
print("Recording complete.")
with open(f"/audio_data{mic.sample_rate}.bin", "wb") as file:
file.write(buffer)
file.flush()
print("Data written to file")Behavior
When using the above code, I find that the audio data is half the expected sample rate when I inspect the data. I.e. recording a 500Hz sine tone using this code, I would expect a 22050Hz sample rate, but on inspection I see a 11025Hz sample rate because the plotted waveform from my saved data has a 1kHz frequency.
Attaching a logic analyzer to the Clock and Data pins, I see that the clock frequency is measured at 705kHz. With the args passed to the ctor to the PDMIn object, I would expect 64*22050 = 1411200 i.e. 1.41120MHz clock frequency.. I think?
Happy to dive deeper and see if I can find out what is going on and submit a PR, but just want to know first if I've misunderstood how it is meant to work! Thanks!
Description
The hardware is a Waveshare Pico Plus board, and the PDM mic is the Adafruit PDM MEMS Microphone
Additional information
No response