nRF52: Analog Audio > SAADC > PDM Module > PCM Mono Audio?

[Shashi]

Hi,

I've read through several posts on this excellent forum for nRF51 on audio.

But, I have the new nRF52 Dev Kit and would like to use an analog signal from a microphone (www.sparkfun.com/.../9964) and stream the mono & low fidelity PCM audio via BLE using the S132 stack.

I was thinking of using SAADC to sample the analog input. But, then, I am not sure how to get the PDM from the SAADC output to feed it in to the PDM module. My goal is to get the PCM output and send it through BLE using S132.

Do I just buy MEMS microphones that give me digital PDM output, instead?

Is this possible? Some guidance and pointers to this novice is much appreciated :)

Thank you..!

• Shashi

[Anders Strand]

Hey.

I doubt that moving saadc samples into the PDM->PCM converter of the PDM module can be done. The PCM conversion happens directly from the input pins. See the nRF52 OPS chapter 41.

The type of microphone you are planning to use will most likely also cause you some issues. By personal experience, i know that they usually have very narrow dynamic range. This means that they can tell between "no sound", and "high sound", but cannot pick up everything in between. Some microphone modules come with adjustable gain, this helps somewhat.

So in conclusion, i would advice you to buy a microphone with PDM output. We also have a i2s module on our nRF52. There exists microphones with this interface as well.

-Anders