E14. Deep Sleep and Power Management

RTC_DATA_ATTR int wakeCount = 0;          // RTC_DATA_ATTR keeps this number during sleep

void setup() {                             // runs at power-on AND every time it wakes
  Serial.begin(115200);                    // start Serial at the ESP32 speed
  delay(500);                              // give the USB link time to start

  wakeCount = wakeCount + 1;               // count this wake-up
  Serial.print("Awake! Wake count: ");     // a label
  Serial.println(wakeCount);               // the count

  Serial.println("Sleeping for 5 seconds"); // say what happens next
  Serial.flush();                          // finish sending before sleeping
  esp_sleep_enable_timer_wakeup(5000000);  // wake after 5,000,000 microseconds = 5 seconds
  esp_deep_sleep_start();                  // sleep now
}

void loop() {                              // never reached - waking restarts setup()
}

#include <driver/rtc_io.h>                // commands for the pins that work during sleep

const int ledPin = 2;                      // the LED is on GPIO 2

void setup() {                             // runs at power-on AND every time it wakes
  Serial.begin(115200);                    // start Serial at the ESP32 speed
  pinMode(ledPin, OUTPUT);                 // the LED pin is an output

  digitalWrite(ledPin, HIGH);              // LED on: we are awake
  Serial.println("Awake! Sleeping in 2 seconds - press the button to wake me"); // tell the user
  delay(2000);                             // stay awake for 2 seconds
  Serial.flush();                          // finish sending before sleeping

  rtc_gpio_pullup_en(GPIO_NUM_4);          // keep GPIO 4 pulled HIGH while asleep
  esp_sleep_enable_ext0_wakeup(GPIO_NUM_4, 0); // wake when GPIO 4 goes LOW (button pressed)
  esp_deep_sleep_start();                  // sleep now - the LED goes off
}

void loop() {                              // never reached - waking restarts setup()
}