Digital MEMS microphone (IM72D128V01) interface with nrf5430 via PDM

[c3_nithin]

Hi,

   Iam currently working with NRF5340 module for the integration of MEMS microphone (IM72D128V01). need to configure PCM sampling rate as 2KHz.

                .min_pdm_clk_freq =  120000,

                .max_pdm_clk_freq = 160000,

this is the configuration that I have given to configure PCM as 2Khz. but while probing the data and clock pins. Iam able to view the clock but no data out.

 

note: have use the DMIC example code.

1) is there any way to use this microphone (IM72D128V01)?

      attaching the screenshot of MEMs microphone.

2) can u suggest the step to validate the data?

        2.1) how to convert the hex data to audio. and validate?

[sensorbee-dev]

I have been able to use a similar MEMS microphone from Infineon with the 5340. If you want to configure the sampling rate to 2 KHz you should set the pcm_rate field in the dmic_cfg structure:

cfg.streams[0].pcm_rate = <SAMPLE_RATE>;

Regarding point number 2, you could stream the 16-bit data over the serial port and have a python script convert it into a .wav file. You should then be able to listen to the recorded data or analyze it using some kind of software.

Also I think the maxmium and minimum clk frequencies you have specified are incorrect. They should reflect the microphone's specification, which I think, if reading the datasheet correctly is 440 KHz to 5.04 Mhz.

[c3_nithin]

thanks for the reply.

1) is there any way to down sample (pcm) using any api?

         

[sensorbee-dev]

Are you referring to the conversion between PDM to PCM? Because the DMIC api will do this for you. dmic_read will give you a "usable" format (PCM) that can be directly used to create a .wav file.

Does this answer your question or did I misinterpet it?

[c3_nithin]

how we create the .wave file .. can u explain in detail. 
share example if any.

[sensorbee-dev]

This code should work, it has been a while since I used it. I think it expects binary data (not hex string). I hope this helps.

import serial
import numpy as np
from scipy.io import wavfile

# Configuration: duration in seconds and sampling rate in Hz
duration = 5  # Record for 5 seconds
Fs = 2000    # Sampling rate of 2000 Hz

# Open the serial port
ser = serial.Serial('/dev/ttyACM0', baudrate=115200, timeout=1)

# Number of samples to read (calculated from duration and sampling rate)
num_samples = int(duration * Fs)

# Buffer to store audio data
audio_data = np.zeros(num_samples, dtype=np.int16)

bytes_per_sample = 2
samples_read = 0
i = 0

# Read audio data from the serial port
while i < num_samples:
    # Read two bytes (16-bit integer)
    data_bytes = ser.read_all()
    
    # Ensure there are exactly 2 bytes to read
    if len(data_bytes) % 2 != 0:
        print(f"Error: {len(data_bytes)} bytes read")
        continue

    # Convert bytes to integer (little-endian)
    for j in range(0, len(data_bytes), bytes_per_sample):
        sample = int.from_bytes(data_bytes[j:j+bytes_per_sample], byteorder='little', signed=True)
        audio_data[i] = sample
        i += 1
    
    # Increment the number of samples read
    samples_read += len(data_bytes) / bytes_per_sample

# Close the serial port
ser.close()

# Path to the output file
output_file = 'output.wav'

# Write to .wav file
wavfile.write(output_file, Fs, audio_data)

print(f"Audio data saved to {output_file}")