Hello,
We have an nrf5340 custom board with the MP23DB02MM PDM mic connected directly to the nrf5340 (CLK to pin0.18 and DOUT to pin0.19). We are reading audio using the DMIC library and sending the PCM data over NUS to a development kit which forwards the data over UART (using the central UART sample). We are running the PDM CLK at 0.768 MHz (12kHz sample rate with D=64) and I have verified with an oscilloscope that the PDMCLKCTRL is being set correctly by the DMIC driver and PDM CLK frequency is correct. The received data always looks like a bit of static followed by values very close to zero (you can't hear anything), but when I look at the DOUT waveform on an oscilloscope it doesn't look like mostly zero. I've attached some sample data binary along with the project (adapted from the Zephyr DMIC example) and pictures of the oscilloscope. I have also monitored the bitrate on the Bluetooth receiving side and verified that there is no data loss.
Unfortunately I can't share the board file but here are the parts relevant to the PDM module:
&clock {
hfclkaudio-frequency = <12288000>;
};
dmic_dev: &pdm0 {
compatible = "nordic,nrf-pdm";
status = "okay";
pinctrl-0 = <&pdm0_default>;
pinctrl-names = "default";
clock-source = "ACLK";
};
&gpio0 {
status = "okay";
mic_lr_pin {
gpio-hog; //pull pin low at boot
gpios = <17 GPIO_ACTIVE_HIGH>;
output-low;
};
};
pdm0_default: pdm0_default {
group1 {
psels = <NRF_PSEL(PDM_CLK, 0, 18)>, <NRF_PSEL(PDM_DIN, 0, 19)>;
};
};
I'm not sure where I'm going wrong so anyone could try and reproduce the issue it would be much appreciated.
Tony
