HighRatePDMSerialPlotterFFT.ino

/**
   @file HighRatePDMSerialPlotterFFT.ino
   @author rakwireless.com
   @brief This example reads audio data from the PDM microphones, and prints
   out the FFT transfer samples to the Serial console. The Serial Plotter built into the
   Arduino IDE can be used to plot the audio data (Tools -> Serial Plotter)
   @note  This example need use the microphones that can supports higher sampling rate.
   @version 0.1
   @date 2022-06-6
   @copyright Copyright (c) 2022
*/
#include <Arduino.h>
#ifdef NRF52_SERIES
#include <Adafruit_TinyUSB.h>
#endif

#include "audio.h" // Click here to install the library: http://librarymanager/All#RAKwireless-Audio

// Audio sample buffers used for analysis and display
int approxBuffer[BUFFER_SIZE];   // ApproxFFT sample buffer
const double samplingFrequency = 48000;
int channels = 1;
// buffer to read samples into, each sample is 16-bits
short sampleBuffer[BUFFER_SIZE];

int print_string[500] = {0};

volatile uint8_t read_flag = 0;
void onPDMdata();

void setup() {

  pinMode(WB_IO2, OUTPUT);
  digitalWrite(WB_IO2, HIGH);
  delay(500);
  pinMode(LED_GREEN, OUTPUT);
  digitalWrite(LED_GREEN, HIGH);
  pinMode(LED_BLUE, OUTPUT);
  digitalWrite(LED_BLUE, HIGH);

  time_t timeout = millis();
  Serial.begin(115200);
  while (!Serial)
  {
    if ((millis() - timeout) < 3000)
    {
      delay(100);
    }
    else
    {
      break;
    }
  }
  // configure the data receive callback
  PDM.onReceive(onPDMdata);
  PDM.setPins(PDM_DATA_PIN, PDM_CLK_PIN, PDM_PWR_PIN);
  // optionally set the gain, defaults to 20
  PDM.setGain(30);
  // initialize PDM with:
  // - one channel (mono mode)
  // - a 200 kHz sample rate
  if (!PDM.begin(channels, PCM_48000)) {
    Serial.println("Failed to start PDM!");
    while (1) yield();
  }
  delay(500);
  Serial.println("=====================FFT example =====================");
}

static int first_flag = 0;
void loop() {
  // wait for samples to be read
  if (read_flag == 1) {
    read_flag = 0;

    // Fill the buffers with the samples
    for (int i = 0; i < BUFFER_SIZE; i++) {
      approxBuffer[i] = sampleBuffer[i];
      //       Serial.println(approxBuffer[i]);
    }

    if (first_flag > 5) //because the all of first IRQ read data is 0
    {
      Approx_FFT(approxBuffer, BUFFER_SIZE, samplingFrequency);
      //      for (int j=0; j<BUFFER_SIZE; j++){
      //        Serial.println(approxBuffer[j]);
      //      }
      memset(print_string, 0, sizeof(print_string));
      memcpy(print_string, approxBuffer, sizeof(approxBuffer));

      for (int j = 0; j < 500; j++)
      {
        Serial.println(print_string[j]);
      }
      delay(1000);
    }
    else
    {
      first_flag++;
    }
  }
}
void onPDMdata() {
  // read into the sample buffer
  PDM.read(sampleBuffer, BUFFER_SIZE * 2);
  read_flag = 1;
}