💤 ESP32 Deep Sleep Won't Wake - Complete Fix Guide

• 📌 No Wake Source Configured – esp_sleep_enable_timer_wakeup() not called
• 📌 Wrong GPIO for External Wake – Using RTC IO pin incorrectly
• 📌 Wake Level Mismatch – HIGH vs LOW trigger level
• 📌 RTC Memory Corruption – Variables stored in RTC memory not preserved
• 📌 Touch Sensor Not Calibrated – Touch wake thresholds wrong
• 📌 ULP Program Not Running – ULP coprocessor program not loaded or configured

The simplest deep sleep configuration:

void setup() {
    Serial.begin(115200);
    delay(1000);
    
    // Do your work here
    Serial.println("Woke up! Taking sensor reading...");
    
    // Configure wake up after 10 seconds (10,000,000 microseconds)
    esp_sleep_enable_timer_wakeup(10 * 1000000);
    
    Serial.println("Entering deep sleep for 10 seconds...");
    
    // Go to deep sleep
    esp_deep_sleep_start();
}

void loop() {
    // This will never run
}

Wake ESP32 when a GPIO pin changes state:

Which GPIOs can wake ESP32?

// GPIO 33 is an RTC IO pin - can wake from deep sleep
#define WAKE_PIN 33

void setup() {
    Serial.begin(115200);
    delay(1000);
    
    // Configure wake pin
    // Wake when pin goes HIGH (button press)
    esp_sleep_enable_ext0_wakeup(WAKE_PIN, HIGH);
    
    // Or use ext1 for multiple pins:
    // esp_sleep_enable_ext1_wakeup(BIT(WAKE_PIN), ESP_EXT1_WAKEUP_ANY_HIGH);
    
    Serial.println("Going to sleep. Press button on GPIO 33 to wake.");
    
    esp_deep_sleep_start();
}

void loop() {}

// Touch pins: T0(GPIO4), T1(GPIO0), T2(GPIO2), T3(GPIO15), 
// T4(GPIO13), T5(GPIO12), T6(GPIO14), T7(GPIO27), T8(GPIO33), T9(GPIO32)

#define TOUCH_PIN T0  // GPIO4

void setup() {
    Serial.begin(115200);
    delay(1000);
    
    // Calibrate touch threshold (run once, save value)
    int touchValue = touchRead(TOUCH_PIN);
    Serial.print("Touch value: ");
    Serial.println(touchValue);
    
    // Set threshold lower than normal reading
    // Normal: ~50, Touched: ~20
    touchSleepWakeUpEnable(TOUCH_PIN, 40);
    
    Serial.println("Touch to wake...");
    esp_deep_sleep_start();
}

void loop() {}

Variables stored in RTC memory survive deep sleep:

// Variables in RTC memory keep their value across sleep
RTC_DATA_ATTR int bootCount = 0;

void setup() {
    Serial.begin(115200);
    delay(1000);
    
    // Increment boot counter (survives deep sleep)
    bootCount++;
    Serial.print("Boot number: ");
    Serial.println(bootCount);
    
    // Get wakeup reason
    esp_sleep_wakeup_cause_t wakeup_reason = esp_sleep_get_wakeup_cause();
    
    switch(wakeup_reason) {
        case ESP_SLEEP_WAKEUP_TIMER:
            Serial.println("Woke by timer");
            break;
        case ESP_SLEEP_WAKEUP_EXT0:
            Serial.println("Woke by GPIO button");
            break;
        case ESP_SLEEP_WAKEUP_TOUCH:
            Serial.println("Woke by touch");
            break;
        default:
            Serial.println("First boot or other wake");
    }
    
    // Configure 10 second timer wake
    esp_sleep_enable_timer_wakeup(10 * 1000000);
    
    Serial.println("Going to sleep...");
    esp_deep_sleep_start();
}

The ULP (Ultra Low Power) coprocessor can read sensors while main CPU sleeps:

// ULP example: Wake when temperature exceeds threshold
// This requires ULP RISC-V assembly programming (advanced)

// For simpler use, OceanRemote handles ULP automatically
// when you enable "Deep Sleep" mode in device configuration

Use this diagnostic sketch to verify wake configuration:

#include "esp_sleep.h"

void setup() {
    Serial.begin(115200);
    delay(1000);
    
    // Print wakeup reason from last sleep
    print_wakeup_reason();
    
    // Test: Configure timer wake
    esp_sleep_enable_timer_wakeup(10 * 1000000);
    
    // Test: Configure GPIO wake on pin 33
    // esp_sleep_enable_ext0_wakeup(GPIO_NUM_33, HIGH);
    
    Serial.println("Sleeping for 10 seconds...");
    esp_deep_sleep_start();
}

void print_wakeup_reason() {
    esp_sleep_wakeup_cause_t wakeup_reason = esp_sleep_get_wakeup_cause();
    
    switch(wakeup_reason) {
        case ESP_SLEEP_WAKEUP_UNDEFINED:
            Serial.println("First boot or reset (not wake from sleep)");
            break;
        case ESP_SLEEP_WAKEUP_EXT0:
            Serial.println("Wakeup caused by external signal using RTC_IO");
            break;
        case ESP_SLEEP_WAKEUP_EXT1:
            Serial.println("Wakeup caused by external signal using RTC_CNTL");
            break;
        case ESP_SLEEP_WAKEUP_TIMER:
            Serial.println("Wakeup caused by timer");
            break;
        case ESP_SLEEP_WAKEUP_TOUCHPAD:
            Serial.println("Wakeup caused by touchpad");
            break;
        case ESP_SLEEP_WAKEUP_ULP:
            Serial.println("Wakeup caused by ULP program");
            break;
        default:
            Serial.print("Wakeup reason: ");
            Serial.println(wakeup_reason);
    }
}

void loop() {}

• Using non-RTC GPIO for wake – Only specific pins can wake ESP32
• Forgetting to enable wake source – Must call esp_sleep_enable_* before esp_deep_sleep_start()
• Serial.print after sleep – Serial may not be ready immediately on wake
• Not adding delay on wake – Add delay(1000) for Serial to initialize
• Using WiFi in deep sleep – WiFi turns off in deep sleep
• No pull-up/pull-down on wake pins – Floating pins cause random wakes

#include "esp_sleep.h"
#include "DHT.h"

#define DHTPIN 4
#define DHTTYPE DHT22

DHT dht(DHTPIN, DHTTYPE);
RTC_DATA_ATTR int bootCount = 0;

void setup() {
    Serial.begin(115200);
    delay(1000);
    
    bootCount++;
    
    // Print wake reason
    esp_sleep_wakeup_cause_t wakeup_reason = esp_sleep_get_wakeup_cause();
    if (wakeup_reason != ESP_SLEEP_WAKEUP_TIMER) {
        Serial.println("First boot - starting sensor readings");
    }
    
    // Read sensor (takes 2-3 seconds)
    dht.begin();
    float temp = dht.readTemperature();
    float humidity = dht.readHumidity();
    
    if (!isnan(temp)) {
        Serial.print("Temperature: ");
        Serial.print(temp);
        Serial.println("°C");
        // Send to OceanRemote or other service here
    }
    
    // Configure timer wake for 5 minutes (5 * 60 * 1000000)
    esp_sleep_enable_timer_wakeup(300 * 1000000);
    
    Serial.print("Deep sleep for 5 minutes. Boot count: ");
    Serial.println(bootCount);
    
    esp_deep_sleep_start();
}

void loop() {}

• Use RTC GPIO pins (0,2,4,12-15,25-27,32,33) for external wake
• Add pull-up or pull-down resistors to wake pins to prevent false triggers
• Store persistent data in RTC_DATA_ATTR variables
• Add delay(1000) at start of setup() for Serial to initialize
• Use esp_sleep_get_wakeup_cause() to debug wake sources
• Consider hibernation mode for maximum battery life (2.5µA)
• Test with short wake intervals (10 seconds) during development

• ESP32 Low Memory Crash
• ESP32 GPIO Not Working
• Power Supply Not Enough Current
• ESP32 Random Reset/Reboot

OceanRemote's deep sleep mode includes:

• ✓ Configurable wake intervals
• ✓ Automatic sensor reading
• ✓ Data upload on wake
• ✓ Months of battery life
• ✓ No coding required