Need Help with nRF52840 PDM Microphone Data Processing

[rashfords]

Hello, I am currently working on a PDM microphone project using nRF52840 and Zephyr RTOS. I've been testing the official Zephyr sample (located at dmicncs/v2.9.0/zephyr/samples/drivers/audio/dmic).

I noticed that the official example sets the PCM sample rate to 16,000 Hz, but when I try to lower it to 8,000 Hz, the hardware doesn't seem to match properly. Does the nRF52840 not support this sample rate?

Additionally, the official example converts the data into PCM format and stores it in a buffer. Do you have any sample code that sends this buffer data over UART?

[Menon]

Hello,

I noticed that the official example sets the PCM sample rate to 16,000 Hz, but when I try to lower it to 8,000 Hz, the hardware doesn't seem to match properly. Does the nRF52840 not support this sample rate?

I have some confusion about whether 8 kHz can be achieved. I will get back to you on this.

Kind Regards,

Abhijith

[rashfords]

do you have an answer

[Hieu]

Hi rashfords,

Please refer to the PDM section of the nRF52840 Product Specification. It can only support 16kHz sample rate.

I would expect the driver to return an error when you try to set 8kHz. Did you check the return code?

Hieu