MP34DT05 Sensor PDM output issue

Nikhil D&K · ‎2021-05-27

Hello,

I am trying to interface MP34DT05 - MEMS Audio sensor in mono configuration to read audio samples from sensor.

Basic working of PDM Audio sensor states that, the analog signal will be sampled at PDM CLK frequency and outputted as pulse modulated bit stream at CLK frequency.

Here is my sensor connections:

-Sensor Vcc to 3V (in range as per datasheet)

-Sensor GND to GND

-Sensor SCLK pin to CLK pin of kit

-Sensor DOUT pin to DIN pin of kit

-Sensor LRCLK pin i havent connected as it's grounded internally as per datasheet. Even if i connect it to GND /VDD externally nothing changes.

So as per the datasheet of MP34DT05 minimum PDM CLK frequency input is 1.2MHz and typical is 2.4MHz. And also the startup time required by the sensor is 10ms (as per datasheet). So when i apply the 1.2MHz, the PDM sensor should output the pulse modulated bit stream at same CLK frequency. But in my case the output bit stream is mostly constant bit values with approx 10 percent duty cycle.

Below is the analyzer output for the sensor and sensor with PDM Clock:

Sensor Output:

Sensor with PDM Clock:

I have also tried testing at 2.4MHz, but just the frequency changes the output remains constant there as well.

So what can be the issue here ? Is my sensor malfunctioning or i am doing something terribly wrong ?

Note: The kit with which i have tried to interface sensor is Nucleo-L4R5ZI and also with Nordic nRF52840 DK but both without any success and with same issue.

For reference:

https://devzone.nordicsemi.com/f/nordic-q-a/75483/nrfx-based-pdm-to-pcm-implementation-i2s-example/312043#312043

niccolò · ‎2021-06-08

Hi @NK.13omalan ,

are you only watching the signal with a digital analyzer?

maybe if you feed the pulse stream to a decoding library the signal is just what you expect.

there is a series of tutorial videos available online on microphone integration.

I would suggest to check out these.

Niccolò