Forward decimated PCM-output from a digital microphone

[MortenBech]

Hi, I'm using the nRF52840 Preview DK to get data from a digital microphone via a PDM interface.

I'm using a clock frequency on 1.032 MHz to activate the microphone.

The data received on the data_in pin seems to be alright.

I have been using this PDM-interface: http://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.nrf52840.ps%2Fpdm.html


Here is my problem:

It seems like the interface includes a decimation filter to produce a PCM-output. By default the PCM-output is sent to the RAM via the EasyDMA. I want to send this PCM data to an external GSM-module that has a PCM-input, so the data recorded by the microphone will be played by its speaker.

Is there any way to access this PCM-output on the nRF52840?

Am I able to connect the PCM-output to a GPIO?

Regards,
Morten

[Bjørn Kvaale]

Hi Morten,

Have you taken a look at the Thingy SDK code? The Thingy:52 microphone uses ADPCM, which is then converted to PCM in the Android/iOS Thingy app. When streaming voice data from the smartphone to the Thingy:52, 8-bit PCM data is sent over BLE to the Thingy:52, which outputs the 8-bit PCM data.

I would recommend taking a look at the drv_speaker.h file. See this documentation too.

Kind Regards,

Bjørn