RE: Interfacing PDM Mic with NRF52832

Kenneth — Tue, 05 Aug 2025 08:18:12 GMT

Hi,

Maybe looking at the hardware description and register values may help here:
https://docs.nordicsemi.com/bundle/ps_nrf52832/page/pdm.html#register.PDMCLKCTRL

Kenneth

RE: Interfacing PDM Mic with NRF52832

Tarunraj Singh — Tue, 29 Jul 2025 14:43:09 GMT

Actually, I am receiving the data and I can see it over the Serial terminal. Today, I checked the clock frequency that my controller is generating. PDM Mic needs 1Mhz to 3Mhz of clock frequency. I am setting it by pdm_cfg.clock_freq = NRF_PDM_FREQ_1032K;

However, the clock is not generating properly. I have observed that when I set the
pdm_cfg.clock_freq = NRF_PDM_FREQ_DEFAULT; it is generating the 5Khz
pdm_cfg.clock_freq = NRF_PDM_FREQ_1032K; it is generating the 30Khz
pdm_cfg.clock_freq = NRF_PDM_FREQ_1067K; it is generating the 70Khz

which is incorrect.
I would really appreciate the help to enable the High Frequency Clock to generate at least 1MHz of frequency.

My code to generate the clock:-

#include "nrf.h"
#include "nrf_delay.h"

// PDM CLK and DIN pin selection
#define PDM_CLK_PIN 23
#define PDM_DIN_PIN 25

// Dummy buffer for PDM DMA (required)
static int16_t dummy_buf[64];

// Start High Frequency Clock (16 MHz crystal)
void hfclk_start(void) {
NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
NRF_CLOCK->TASKS_HFCLKSTART = 1;
while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);
}

void pdm_init(void) {
// Route CLK and DIN pins
NRF_PDM->PSEL.CLK = PDM_CLK_PIN;
NRF_PDM->PSEL.DIN = PDM_DIN_PIN;

// Use 16x PDM clock ratio → ~1.067 MHz
NRF_PDM->PDMCLKCTRL = PDM_PDMCLKCTRL_FREQ_1067K; // 16 MHz / 15 = 1.067 MHz

// Configure for Mono input, Left channel, falling edge
NRF_PDM->MODE = (PDM_MODE_OPERATION_Mono << PDM_MODE_OPERATION_Pos) |
(PDM_MODE_EDGE_LeftFalling << PDM_MODE_EDGE_Pos);

// Dummy buffer for DMA, 64 samples
NRF_PDM->SAMPLE.PTR = (uint32_t)dummy_buf;
NRF_PDM->SAMPLE.MAXCNT = 64;

// Enable the PDM peripheral
NRF_PDM->ENABLE = PDM_ENABLE_ENABLE_Enabled << PDM_ENABLE_ENABLE_Pos;

// Start the PDM clock and sampling
NRF_PDM->TASKS_START = 1;
}

int main(void) {
hfclk_start(); // Ensure the external 16 MHz oscillator is started
pdm_init(); // Setup and start PDM

while (1) {
nrf_delay_ms(1000); // Do nothing, just keep the system running
}
}

Thank You!!!

RE: Interfacing PDM Mic with NRF52832

Vidar Berg — Tue, 29 Jul 2025 11:46:14 GMT

Hello,

The code snippet you posted doesn't show that you're initializing the pdm_buffer[] array, as far as I can tell. In that case, it will just be zero initialized by the startup code.

Best regards,

Vidar