sonometre.ino
The Plus2's PDM mic samples at 16 kHz: RMS and peak fall out of one loop and show as a colored bar. The red threshold at 85% matches a loud conversation at one meter.
Hardware required
An M5StickC Plus2 (ESP32-PICO-V3-02, 135×240 display, A/B/C buttons, passive buzzer on G2, IR + red LED on G19, MPU6886 IMU, microphone, 200 mAh battery). None; a sound source to test.
Wiring
No wiring — MEMS mic inside the case, behind its hole.
How it works
Mic.record fills a signed 16-bit buffer; the sum of squares gives RMS, the max gives peak. The /100 mapping is an ear setting, not a dB standard. In the Arduino IDE (esp32 package), board « M5StickCPlus2 »; « M5StickCPlus2 » or M5Unified library. On the PMIC-less v2, hold button C for >2 s to power on; HOLD (G4) latches the power.
Going further
Audio warning (buzzer above threshold), or a day-long noise logger timestamping peaks.
sonometre.ino
// Micro SPM1423 (PDM) via M5Unified : niveau 0-100 en barre.
#include <M5Unified.h>
const int N = 1024;
int16_t tampon[N];
void setup() {
auto cfg = M5.config();
M5.Mic.setSampleRate(16000);
M5.begin(cfg);
M5.Display.setRotation(1);
}
void loop() {
M5.Mic.record(tampon, N, 16000); // 64 ms de 16 bits
long long somme = 0;
int16_t crete = 0;
for (int i = 0; i < N; i++) {
somme += (long)tampon[i] * tampon[i];
crete = max(crete, (int16_t)abs(tampon[i]));
}
float rms = sqrtf((float)somme / N);
int niveau = constrain((int)(rms / 100), 0, 100);
M5.Display.fillRect(0, 0, 240, 135, TFT_BLACK);
M5.Display.fillRect(4, 100, 232 * niveau / 100, 24,
niveau > 85 ? TFT_RED : TFT_GREEN);
M5.Display.setCursor(4, 20);
M5.Display.printf("RMS %6.0f crete %d\n", rms, crete);
M5.Display.printf("niveau %d %%\n", niveau);
delay(100);
}