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：
测试视频可以在B站看到：
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();
}
最终成品的测试视频：
参考：
- https://www.dfrobot.com.cn/goods-3220.html
- https://wiki.dfrobot.com.cn/_SKU_SEN0487_Fermion_MEMS_Microphone_Sensor
