pdm_rec

MEMS Digital Microphone(PDM) Recording Program for Raspberry Pi

Record on memory, and output to stdout.

Install

gcc -O2 -o pdm_start pdm_start.c pi_perif.c
gcc -O2 -o pdm_rec pdm_rec.c pi_perif.c
sudo cp pdm_start /usr/bin/
sudo cp pdm_rec /usr/bin/

Usage

connect MEMS Microphone GPIO 18 is PCM_CLK GPIO 20 is PCM_DIN

You Must run pdm_start befor pdm_rec

sudo pdm_satrt clock(MHz) Example : sudo pdm_start 4.8

The actual clock will not exceed the specified value.

sudo pdm_rec duration ch

duration(sec) is limited by memory. ch: ch1 | ch2 | ch1+2

prevent overflow error, use chrt

for example:

sudo pdm_start 2.4
sudo chrt -f 99 pdm_rec 180 ch1 > rec01.dat

rec01.dat is

• 180sec monoral
• fs = 2.4MHz/16 = 150kHz
• 16bit signed LitteEndian
• RAW data

convert to audio file

use SOX. example: convert to 44.1kHz flac, gain +20dB

sox -t raw -c 1 -r 150000 -e s -b 16 rec01.dat  -b 24 -r 44100 rec01.flac gain 20