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  • Case ID: 343284
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Higher rate PDM not working

Geoffr

Hi,

We are trying to provide example support for our RAK4631 (nRF52840 based) and an ultrasonic PDM microphone (RAK18032). We have been able to get a sample frequency of 100 kHz at 16bits working, but not 200 kHz. We are trying to do this in Mono mode. At 200 kHz we don't seem to get any valid data (FFTs are completely wrong)

We are using the PDM library from Arduino which provides support for up to 200 kHz.

100 kHz PCM = 8000K PDM
200 kHz PCM = 16000K PDM

Has anyone been able to get this working? We need to get this working for customers trying to monitor wildlife (eg Bats).

If this has been confirmed to work I can post our sample code as necessary. 

Thanks!

Parents
  • 0

    Perhaps use a debugger to see what the PDM library is setting the PDMCLKCTRL control register to, as 1600kHz is not listed as a recommended setting. However, it may work using this helpful information from a recent post:

    nrf52-pdm-frequency-calculation posted by guilherme

  • 0 in reply to hmolesworth

    Hi,
    Thank you for your quick response.
      PDMCLKCTRL = 0x80000000UL
    I tested this formula and it doesn't correspond to the values in the manual. Do you know what could be the reason?

    During debugging, it was found that when configured to 200KHZ, PDM_IRQHandler no longer entered, which means that no PDM interrupts were generated, but when configured to 100KHZ, interrupts could be generated normally.
    What are the typical reasons why PDM no longer generates interrupts?

    BR 

    Michael

  • 0 in reply to MichaelHao

    Hi!

    Only the values listed in the PS have been fully and thoroughly tested. If you are using values that are not listed in the PS, we cannot guarantee that they will work and it will be on your own risk.

Reply
  • 0 in reply to MichaelHao

    Hi!

    Only the values listed in the PS have been fully and thoroughly tested. If you are using values that are not listed in the PS, we cannot guarantee that they will work and it will be on your own risk.

Children
  • 0 in reply to Sigurd

    Hi!
    Could you please tell me what PS means Product sheet?
    Does it mean I can only take the values ​​in the blue box?

    Thank you!

  • 0 in reply to MichaelHao

    Hi,

    MichaelHao said:
    Could you please tell me what PS means Product sheet?

    PS=product specification

    MichaelHao said:
    Does it mean I can only take the values ​​in the blue box?

    Correct.

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