Hello, I’m currently working on a PDM microphone project using the nRF52840 and the Zephyr RTOS. I’ve been testing the official dmic example from Zephyr (located at ncs/v2.9.0/zephyr/samples/drivers/audio/dmic).
The code seems to capture microphone data into a buffer zone, but when I send this data over UART for analysis, I observe periodic large fluctuations in the values like this:
The sample rate is set to 16000, and through the oscilloscope I observed that the PDM clock signal is 1.28MHz.In the code, #define SAMPLE_BIT_WIDTH 16, so I guess it is internally converted to hexadecimal characters and send. I’m unsure about what does the raw output from this example represent? Is it PCM samples, or still PDM, or something else? And how can I convert this data into audible sound? I need an idea.
In dmic_nrfx_pdm.c, the clock frequency seems to be limited