FireBeetle 显示环境声音频谱 · Fermion MEMS 麦克风模块

前一段入手了Fermion:全向MEMS麦克风模块（SEN0487），这款模块非常简单能够直接输出模拟信号。简单之处在于无需外部元件进行放大，当没有检测到声音时，输出电压在1.5V左右浮动，在说话时通过ADC采样可以很容易看到声音的波形。

首先跑了一下WIKI给出的示例文件，使用 Arduino 自带的串口绘图工具查看了一下波形：

可以看到内部自带了滤波，敏感度也不错。

接下来，配合之前多次使用的 12864 OLED制作一个频谱显示装置。代码参考 https://github.com/s-marley/ESP32_FFT_VU了。硬件部分除了供电的 VCC和GND, 只需要将模块输出连接到A0（IO36）即可。

#include <arduinoFFT.h>
#include "DFRobot_OLED12864.h"

// 12864 OLED 配置
#define I2C_addr 0x3c
#define pin_SPI_cs D2

#define SAMPLES         1024          // Must be a power of 2
#define SAMPLING_FREQ   40000         // Hz, must be 40000 or less due to ADC conversion time. Determines maximum frequency that can be analysed by the FFT Fmax=sampleF/2.
#define AMPLITUDE       1000          // Depending on your audio source level, you may need to alter this value. Can be used as a 'sensitivity' control.
#define AUDIO_IN_PIN    A0            // Signal in on this pin

#define NOISE           500           // Used as a crude noise filter, values below this are ignored
const uint8_t kMatrixWidth = 16;                          // Matrix width
const uint8_t kMatrixHeight = 16;                         // Matrix height

#define NUM_BANDS       16            // To change this, you will need to change the bunch of if statements describing the mapping from bins to bands

#define BAR_WIDTH      (kMatrixWidth  / (NUM_BANDS - 1))  // If width >= 8 light 1 LED width per bar, >= 16 light 2 LEDs width bar etc
#define TOP            (kMatrixHeight - 0)                // Don't allow the bars to go offscreen

DFRobot_OLED12864 OLED(I2C_addr, pin_SPI_cs);

// Sampling and FFT stuff
unsigned int sampling_period_us;
byte peak[] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}; // The length of these arrays must be >= NUM_BANDS
int oldBarHeights[] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
int bandValues[] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
double vReal[SAMPLES];
double vImag[SAMPLES];
unsigned long newTime;

arduinoFFT FFT = arduinoFFT(vReal, vImag, SAMPLES, SAMPLING_FREQ);

void setup() {
  Serial.begin(115200);

  OLED.init();
 // OLED.flipScreenVertically();

  sampling_period_us = round(1000000 * (1.0 / SAMPLING_FREQ));
}

unsigned long int Elsp1;
int h[16];

void loop() {

  // Reset bandValues[]
  for (int i = 0; i < NUM_BANDS; i++) {
    bandValues[i] = 0;
  }

  // Sample the audio pin
  for (int i = 0; i < SAMPLES; i++) {
    newTime = micros();
    vReal[i] = analogRead(AUDIO_IN_PIN); // A conversion takes about 9.7uS on an ESP32
    vImag[i] = 0;
    while ((micros() - newTime) < sampling_period_us) {
      /* chill */
    }
  }

  // Compute FFT
  FFT.DCRemoval();
  FFT.Windowing(FFT_WIN_TYP_HAMMING, FFT_FORWARD);
  FFT.Compute(FFT_FORWARD);
  FFT.ComplexToMagnitude();

  // Analyse FFT results
  for (int i = 2; i < (SAMPLES / 2); i++) {    // Don't use sample 0 and only first SAMPLES/2 are usable. Each array element represents a frequency bin and its value the amplitude.
    if (vReal[i] > NOISE) {                    // Add a crude noise filter

      //16 bands, 12kHz top band
      if (i <= 2 )           bandValues[0]  += (int)vReal[i];
      if (i > 2   && i <= 3  ) bandValues[1]  += (int)vReal[i];
      if (i > 3   && i <= 5  ) bandValues[2]  += (int)vReal[i];
      if (i > 5   && i <= 7  ) bandValues[3]  += (int)vReal[i];
      if (i > 7   && i <= 9  ) bandValues[4]  += (int)vReal[i];
      if (i > 9   && i <= 13 ) bandValues[5]  += (int)vReal[i];
      if (i > 13  && i <= 18 ) bandValues[6]  += (int)vReal[i];
      if (i > 18  && i <= 25 ) bandValues[7]  += (int)vReal[i];
      if (i > 25  && i <= 36 ) bandValues[8]  += (int)vReal[i];
      if (i > 36  && i <= 50 ) bandValues[9]  += (int)vReal[i];
      if (i > 50  && i <= 69 ) bandValues[10] += (int)vReal[i];
      if (i > 69  && i <= 97 ) bandValues[11] += (int)vReal[i];
      if (i > 97  && i <= 135) bandValues[12] += (int)vReal[i];
      if (i > 135 && i <= 189) bandValues[13] += (int)vReal[i];
      if (i > 189 && i <= 264) bandValues[14] += (int)vReal[i];
      if (i > 264          ) bandValues[15] += (int)vReal[i];
    }
  }

  // Process the FFT data into bar heights
  for (byte band = 0; band < NUM_BANDS; band++) {

    // Scale the bars for the display
    int barHeight = bandValues[band] / AMPLITUDE;
    if (barHeight > TOP) barHeight = TOP;

    // Small amount of averaging between frames
    barHeight = ((oldBarHeights[band] * 1) + barHeight) / 2;

    // Move peak up
    if (barHeight > peak[band]) {
      peak[band] = min(TOP, barHeight);
    }
    h[band] = barHeight;

    // Save oldBarHeights for averaging later
    oldBarHeights[band] = barHeight;

  }

  if (millis() - Elsp1 > 60) {
    for (byte band = 0; band < NUM_BANDS; band++)
      if (peak[band] > 0) peak[band] -= 1;
      
    Elsp1 = millis();
  }
  /*
       //直接输出 FFT 结果
       for (int i=0;i<16;i++) {
         if (bandValues[i]<16) {Serial.print(" ");}
         Serial.print(bandValues[i],HEX);
         Serial.print(" ");
       }
       Serial.println("");
  */

  // 擦除上一次
  OLED.clear();  
  for (int i = 0; i < 16; i++) {
   OLED.fillRect(8 * (16-i), 0, 8, 4 * h[i]);
   OLED.fillRect(8 * (16-i), peak[i]*4, 8, 3);
  }
  
  for (int i = 0; i < 16; i++) {  
    Serial.print(h[i], HEX);
    Serial.print("");
  }
  Serial.println("");
  /*
  for (int i = 0; i < 16; i++) {  
    Serial.print(peak[i], HEX);
    Serial.print("");
  }
  Serial.println("");
  */

  // 显示当前
  OLED.display();
}
复制代码

最终成品的测试视频：

参考：

1. https://www.dfrobot.com.cn/goods-3220.html

2. https://wiki.dfrobot.com.cn/_SKU ... S_Microphone_Sensor

FireBeelte 显示环境声音频谱