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. 

[Nikhil Komalan]

Any suggestions ?

[Audun]

Sorry, I have been thinking about this one for a bit, and I don't have any good ideas. I checked if it could be a VDD supply issue regarding nRF_USB, but I don't think that is a problem. VDD on the headers should be able to supply external circuitry regardless of which USB connection you have used.

I think it would be worthwhile to test another sensor, in case this particular unit is faulty.

To summarize: You've verified that VDD and CLK is within the sensor specification (albeit in the lower end for the clock, but that should not matter), but still the output does not look good. You've also verified that there is no external circuitry messing with the output signal, by disconnecting the data line. I think the next step would be to try another sensor unit.