Deep Sleep & Low-Power Modes

Cutting power draw for battery projects using deep sleep, timers, and wake-on-pin.

Battery-powered ESP32 projects live or die on how well they use deep sleep — a mode where almost everything on the chip is powered down and current draw drops by several orders of magnitude.

#define SLEEP_SECONDS 60

void setup() {
  Serial.begin(115200);
  Serial.println("Taking a reading, then sleeping...");
  // ... read a sensor, send data ...

  esp_sleep_enable_timer_wakeup(SLEEP_SECONDS * 1000000ULL);
  esp_deep_sleep_start();
}

void loop() {
  // never reached — deep sleep restarts the chip on wake
}

What survives sleep

Deep sleep resets most of the chip, including regular variables — setup() runs again from the top on wake, as if the board had just been powered on. Values that need to persist across a sleep cycle must be stored in RTC memory or flash instead of an ordinary variable.

Waking up

A wake can be scheduled with a timer, as above, or triggered by a change on certain GPIO pins — useful for a project that should sleep until a button is pressed or a sensor trips.