Example1_MicrophoneOutput.ino

/* Author: Nathan Seidle
  Created: July 24, 2019
  License: MIT. See SparkFun Arduino Apollo3 Project for more information

  This example demonstrates how to use the pulse density microphone (PDM) on Artemis boards.
  This library and example are heavily based on the Apollo3 pdm_fft example.
*/

//Global variables needed for PDM library
#define pdmDataBufferSize 4096 //Default is array of 4096 * 32bit
uint16_t pdmDataBuffer[pdmDataBufferSize];

//Global variables needed for the FFT in this sketch
float g_fPDMTimeDomain[pdmDataBufferSize * 2];
float g_fPDMFrequencyDomain[pdmDataBufferSize * 2];
float g_fPDMMagnitudes[pdmDataBufferSize * 2];
uint32_t sampleFreq;

//Enable these defines for additional debug printing
#define PRINT_PDM_DATA 0
#define PRINT_FFT_DATA 0

#include <PDM.h> //Include PDM library included with the Aruino_Apollo3 core
AP3_PDM myPDM;   //Create instance of PDM class

//Math library needed for FFT
#define ARM_MATH_CM4
#include <arm_math.h>

void setup()
{
  Serial.begin(115200);
  Serial.println("SparkFun PDM Example");

  if (myPDM.begin(36, 37) == false) // Turn on PDM with default settings, start interrupts
  {
    Serial.println("PDM Init failed. Are you sure these pins are PDM capable?");
    while (1)
      ;
  }
  Serial.println("PDM Initialized");

  printPDMConfig();
}

void loop()
{
  if (myPDM.available())
  {
    myPDM.getData(pdmDataBuffer, pdmDataBufferSize);

    printLoudest();
  }

  // Go to Deep Sleep until the PDM ISR or other ISR wakes us.
  am_hal_sysctrl_sleep(AM_HAL_SYSCTRL_SLEEP_DEEP);
}

//*****************************************************************************
//
// Analyze and print frequency data.
//
//*****************************************************************************
void printLoudest(void)
{
  float fMaxValue;
  uint32_t ui32MaxIndex;
  int16_t *pi16PDMData = (int16_t *)pdmDataBuffer;
  uint32_t ui32LoudestFrequency;

  //
  // Convert the PDM samples to floats, and arrange them in the format
  // required by the FFT function.
  //
  for (uint32_t i = 0; i < pdmDataBufferSize; i++)
  {
    if (PRINT_PDM_DATA)
    {
      Serial.printf("%d\n", pi16PDMData[i]);
    }

    g_fPDMTimeDomain[2 * i] = pi16PDMData[i] / 1.0;
    g_fPDMTimeDomain[2 * i + 1] = 0.0;
  }

  if (PRINT_PDM_DATA)
  {
    Serial.printf("END\n");
  }

  //
  // Perform the FFT.
  //
  arm_cfft_radix4_instance_f32 S;
  arm_cfft_radix4_init_f32(&S, pdmDataBufferSize, 0, 1);
  arm_cfft_radix4_f32(&S, g_fPDMTimeDomain);
  arm_cmplx_mag_f32(g_fPDMTimeDomain, g_fPDMMagnitudes, pdmDataBufferSize);

  if (PRINT_FFT_DATA)
  {
    for (uint32_t i = 0; i < pdmDataBufferSize / 2; i++)
    {
      Serial.printf("%f\n", g_fPDMMagnitudes[i]);
    }

    Serial.printf("END\n");
  }

  //
  // Find the frequency bin with the largest magnitude.
  //
  arm_max_f32(g_fPDMMagnitudes, pdmDataBufferSize / 2, &fMaxValue, &ui32MaxIndex);

  ui32LoudestFrequency = (sampleFreq * ui32MaxIndex) / pdmDataBufferSize;

  if (PRINT_FFT_DATA)
  {
    Serial.printf("Loudest frequency bin: %d\n", ui32MaxIndex);
  }

  Serial.printf("Loudest frequency: %d         \n", ui32LoudestFrequency);
}

//*****************************************************************************
//
// Print PDM configuration data.
//
//*****************************************************************************
void printPDMConfig(void)
{
  uint32_t PDMClk;
  uint32_t MClkDiv;
  float frequencyUnits;

  //
  // Read the config structure to figure out what our internal clock is set
  // to.
  //
  switch (myPDM.getClockDivider())
  {
  case AM_HAL_PDM_MCLKDIV_4:
    MClkDiv = 4;
    break;
  case AM_HAL_PDM_MCLKDIV_3:
    MClkDiv = 3;
    break;
  case AM_HAL_PDM_MCLKDIV_2:
    MClkDiv = 2;
    break;
  case AM_HAL_PDM_MCLKDIV_1:
    MClkDiv = 1;
    break;

  default:
    MClkDiv = 0;
  }

  switch (myPDM.getClockSpeed())
  {
  case AM_HAL_PDM_CLK_12MHZ:
    PDMClk = 12000000;
    break;
  case AM_HAL_PDM_CLK_6MHZ:
    PDMClk = 6000000;
    break;
  case AM_HAL_PDM_CLK_3MHZ:
    PDMClk = 3000000;
    break;
  case AM_HAL_PDM_CLK_1_5MHZ:
    PDMClk = 1500000;
    break;
  case AM_HAL_PDM_CLK_750KHZ:
    PDMClk = 750000;
    break;
  case AM_HAL_PDM_CLK_375KHZ:
    PDMClk = 375000;
    break;
  case AM_HAL_PDM_CLK_187KHZ:
    PDMClk = 187000;
    break;

  default:
    PDMClk = 0;
  }

  //
  // Record the effective sample frequency. We'll need it later to print the
  // loudest frequency from the sample.
  //
  sampleFreq = (PDMClk / (MClkDiv * 2 * myPDM.getDecimationRate()));

  frequencyUnits = (float)sampleFreq / (float)pdmDataBufferSize;

  Serial.printf("Settings:\n");
  Serial.printf("PDM Clock (Hz):         %12d\n", PDMClk);
  Serial.printf("Decimation Rate:        %12d\n", myPDM.getDecimationRate());
  Serial.printf("Effective Sample Freq.: %12d\n", sampleFreq);
  Serial.printf("FFT Length:             %12d\n\n", pdmDataBufferSize);
  Serial.printf("FFT Resolution: %15.3f Hz\n", frequencyUnits);
}