• State Not Answered
  • Replies 14 replies
  • Subscribers 67 subscribers
  • Views 7998 views
  • Users 0 members are here
Attachments (11) Download All
Nordic Case Info
  • Case ID: 270395
Options
This post is older than 2 years and might not be relevant anymore
More Info: Consider searching for newer posts

nRFX based PDM to PCM implementation (I2S example)

Nikhil Komalan

Hello,

I am currently interfacing my nRF52840 DK with i2S based MP34DT05 sensor. I am using nrfx i2s driver's for interfacing with sensor. I am using master clk of 2MHz, LCLK 16KHZ. 

My sensor output PDM data. In my project I am recording audio samples on left channel, so I am currently getting 2*16bit of left data per 32bits as shown in nrf docs. I have got 16bit recorded samples in buffer, but to how to convert this pdm data in pcm format. 

Normally we need to divide the PDM data with a decimation factor, but in I2S we already are dividing the bit sampling rate with ratio value. So is the output from the I2S itself is decimated PCM ?  

Or can anyone give a example of how to convert the PDM to PCM data. Any sort of help is dually appreciated. 

Parents
  • 0
    Nikhil Komalan said:

    L/R pin connection Information

    When i see the nRF52840 PDM docs (Fig 2), it shows i have to connect L/R pin to VDD for left channel, but my sensor say opposite. 

    I wouldn't worry so much about the L/R selection or clock edge details at this stage. In my experience when only one microphone is connected to the PDM peripheral, the data signal will in effect end up in both channels as no other sensor is driving the data line for the other channel. Regardless, you can configure the nrfx pdm driver to sample stereo and sort out the exact channel details later.

    Your hardware setup sounds sensible. The MP34DT05 supply voltage falls within VDD on the nRF52840-DK. I think VDD on nRF52840-DK defaults to 1.8V, but I'm not 100% sure.

    Nikhil Komalan said:
    Okay will also check that and will also use python script on the same. Any others suggestions or guidance is also appreciated.

    In terms of electrical setup, wire length could be an issue.

    In the logic analyzer trace made at the sensor, I also noticed that the two signals seems very similar. It's hard to tell from just this snippet, but could there be a short between the clock and data lines?

    This screenshot below was taken a while ago, but shows the kind of pattern I would expect to see on the PDM clock and data lines:

Reply
  • 0
    Nikhil Komalan said:

    L/R pin connection Information

    When i see the nRF52840 PDM docs (Fig 2), it shows i have to connect L/R pin to VDD for left channel, but my sensor say opposite. 

    I wouldn't worry so much about the L/R selection or clock edge details at this stage. In my experience when only one microphone is connected to the PDM peripheral, the data signal will in effect end up in both channels as no other sensor is driving the data line for the other channel. Regardless, you can configure the nrfx pdm driver to sample stereo and sort out the exact channel details later.

    Your hardware setup sounds sensible. The MP34DT05 supply voltage falls within VDD on the nRF52840-DK. I think VDD on nRF52840-DK defaults to 1.8V, but I'm not 100% sure.

    Nikhil Komalan said:
    Okay will also check that and will also use python script on the same. Any others suggestions or guidance is also appreciated.

    In terms of electrical setup, wire length could be an issue.

    In the logic analyzer trace made at the sensor, I also noticed that the two signals seems very similar. It's hard to tell from just this snippet, but could there be a short between the clock and data lines?

    This screenshot below was taken a while ago, but shows the kind of pattern I would expect to see on the PDM clock and data lines:

Children
No Data
Related