🛠 Réveil par mouvement et économie d'énergie (HOLD/RTC)

Objectives

Put the M5StickC Plus2 v2 to sleep to save the 200 mAh battery and wake it up periodically. The major pitfall of the v2 without a PMIC: power is latched by the HOLD pin (G4); after a wake-up (IRQ from the BM8563 RTC), the firmware must immediately set HOLD=1, otherwise the device turns off again — which looks like a boot loop. Hardware-accelerated wake-up via the MPU6886 INT pin is not documented as being routed to a wake-up pin: >

Hardware

• 1× M5StickC Plus2 (v2) — charged battery
• USB-C cable for uploading (when charging, shutdown is only a screen sleep)
• Arduino IDE / PlatformIO, M5Unified

Complete code

//veille periodique + pique d'acceleration — architecture HOLD (G4) de la v2
#include <M5Unified.h>

const int PIN_HOLD = 4;              // POWER HOLD = G4 (officiel)
const float SEUIL_MOUV = 1.5f;       // g
uint32_t eveils = 0;

void setup {
  pinMode(PIN_HOLD, OUTPUT);
  digitalWrite(PIN_HOLD, HIGH);      // VITAL: garder l'alim apres un reveil RTC
  auto cfg = M5.config;
  M5.begin(cfg);
  M5.Display.setRotation(1);
  M5.Display.setTextSize(2);
  M5.Display.setTextColor(TFT_MAGENTA, TFT_BLACK);
  M5.Display.printf("Reveil #%lu\n", (unsigned long)++eveils);
  delay(400);
}

void loop {
  M5.update;
  float ax, ay, az;
  M5.Imu.getAccel(&ax, &ay, &az);
  float n = sqrtf(ax * ax + ay * ay + az * az);
  if (n > SEUIL_MOUV) {              // mouvement : on reste eveille et on bippe
    M5.Display.setCursor(0, 40);
    M5.Display.printf("MOUVEMENT %4.2f g", n);
    M5.Speaker.tone(1568, 100);
    vTaskDelay(300 / portTICK_PERIOD_MS);
  } else {
    // Pas de mouvement : deep-sleep 2 s (le timer reveille l'ESP32).
    // Sans USB, retirer HOLD eteint vraiment ; avec timer-wakeup, l'ESP
    // redemarre et setup remet HOLD=1.
    esp_sleep_enable_timer_wakeup(2000000ULL);
    esp_deep_sleep_start;
  }
  // Bouton C (G35) : appui long > 6 s sans USB = extinction materielle.
}

Expected verification

The device wakes up every 2 seconds (wake-up counter displayed) and consumes almost nothing between wake-ups. Shaking the stick keeps it awake with peak display and beep. Cutting HOLD (long press C without USB) turns everything off; restarting is done by holding C for more than 2 seconds.

Common errors

• Forgetting digitalWrite(HOLD, HIGH) at the very beginning of setup: after an RTC wake-up, the machine turns off immediately — the "reboot loop" symptom documented by M5Stack.
• Believing that esp_deep_sleep_start is enough to turn off the device: without USB, you must release HOLD (G4=0); classic deep-sleep leaves the power latch active.
• Relying on a hardware interrupt from the IMU: the routing of the MPU6886 INT to a wake-up pin is not confirmed in the documentation.
• Testing "shutdown" while plugged into USB: with USB, a long press of C only turns off the screen — the battery does not drain but the device remains powered.
• The green LED is not programmable: it is a sleep status indicator, not a user LED.