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To put an ESP32 into deep sleep, configure one or more supported wakeup sources with the ESP-IDF sleep APIs, then call esp_deep_sleep_start(). Deep sleep is not a paused program: the CPUs, most RAM, and many digital peripherals power off, so waking starts a fresh boot. Your firmware must identify why the chip woke and restore any state it needs.
This tutorial follows Espressif’s ESP-IDF v6.1 documentation for the ESP32. Pin support and some wakeup restrictions vary by chip variant and revision, so verify your exact device before wiring a wake signal.
What happens when an ESP32 enters deep sleep?
In deep sleep, the CPUs, most RAM, and digital peripherals clocked from APB_CLK are powered off. The RTC controller, ULP coprocessor, and RTC FAST and RTC SLOW memories are among the components that can remain available. When a wake source fires, the application boots again; it does not continue from the instruction after the sleep call.
That reboot is the key design difference from light sleep. In light sleep, digital peripherals, most RAM, and CPUs are clock-gated and their supply voltage is reduced, so their internal states are preserved on exit. Choose light sleep when maintaining execution state matters; choose deep sleep when your firmware can tolerate a new boot and needs the deep-sleep power-down behavior.
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Deep sleep also powers down Wi-Fi and Bluetooth peripherals. Active wireless connections are not maintained. Espressif documents modem sleep with automatic light sleep as the alternative when a connection must be preserved. See Espressif’s ESP-IDF v6.1 sleep modes guide for mode and API details.
What you need before you start
- An ESP32 development board and its pinout.
- The exact chip variant and, where relevant, its revision. Wakeup pin support and source combinations are not identical across devices.
- A plan for what must happen before sleep, which event should wake the chip, and what state the application must recover after reboot.
Do not assume the chip’s sleep behavior gives a particular development board a specific sleep current or battery life. The board’s other components and configuration affect the system-level result; Espressif’s cited guide does not establish a universal board-current figure.
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Which wakeup source should you use?
ESP-IDF supports several wakeup mechanisms. Pick one based on the event you need to detect and the resources your exact chip exposes.
| Wakeup source | Best suited to | Important requirements and limits |
|---|---|---|
| Timer | Waking after an elapsed interval | Configure with esp_sleep_enable_timer_wakeup(); its argument is in microseconds, but effective resolution depends on the RTC slow-clock source. |
| EXT0 or EXT1 | Waking from an external input level | Requires a supported RTC-capable input pin. Check the exact chip’s pinout and documentation; some wakeup combinations conflict, and ESP32 revisions 0 and 1 have additional limitations. |
| GPIO deep-sleep wake | Waking from a supported GPIO signal | The ESP32 guide describes this for pins powered by the VDD3P3_RTC domain. Confirm that the specific pin and chip support it. Do not confuse this deep-sleep mechanism with GPIO wakeup for light sleep. |
| Touchpad | Waking on a configured touch-pad event | Configure the touch-pad interrupt before sleep and check the documented revision-specific behavior and incompatibilities. |
| ULP coprocessor | Monitoring or polling while the main CPU is off | Uses RTC SLOW memory and has power-domain and wake-source combination constraints. |
Espressif allows wakeup sources to be combined, so any enabled compatible source can wake the chip. Check each source’s restrictions before combining them. Sources remain enabled after wake unless you disable them with esp_sleep_disable_wakeup_source(); account for that if later sleep cycles use a different strategy.
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How do you put an ESP32 into deep sleep?
- Confirm your chip and pinout. Identify the precise ESP32 variant and development board. Select only a wake pin supported by that device and its relevant power domain.
- Finish work that cannot continue during sleep. Save or transmit needed data and shut down Wi-Fi and Bluetooth using the calls appropriate to your framework. A deep-sleep cycle will not preserve wireless connections.
- Enable a wakeup source. Call the matching
esp_sleep_enable_*_wakeup()API. For a timer, convert the intended interval to microseconds carefully; the API’s units do not guarantee microsecond timing accuracy. - Enter deep sleep. After checking the selected source’s pin, revision, and power-domain requirements, call
esp_deep_sleep_start(). Espressif’s sleep modes guide points to itssystem/deep_sleepexample for a fuller implementation. - Handle the next boot. Determine the wakeup cause and restore or load any state the application needs. Do not rely on local variables or execution context from before deep sleep.
How do you use timer wakeup?
Enable timer wake with esp_sleep_enable_timer_wakeup(), passing a duration expressed in microseconds, then enter deep sleep. For example, a desired interval of five seconds is represented as 5,000,000 microseconds. This is the API’s requested duration, not a promise that the device will wake with microsecond accuracy: effective timer resolution depends on the selected RTC slow-clock source.
Use the timer when an approximate scheduled wake is the right trigger. If an input event must wake the chip sooner, configure an appropriate external, GPIO, touch, or ULP-based source as well, subject to that source’s compatibility rules.
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What should firmware do after wake?
Treat the wake as a new boot. At startup, inspect the wakeup cause using the ESP-IDF sleep/wakeup facilities, then initialize the application and recover any information that must persist. RTC memory can be retained in deep sleep, but ordinary application state in powered-off RAM cannot be assumed to survive.
If the next cycle uses a different wake source, explicitly disable previously enabled sources as needed with esp_sleep_disable_wakeup_source() before configuring the new strategy. Otherwise, an earlier source may remain active after wake.
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Common deep-sleep mistakes
- Expecting the program to resume. Deep sleep leads to a fresh boot, not a return to the line after
esp_deep_sleep_start(). - Assuming every pin can wake the chip. Confirm RTC capability, power domain, chip variant, and board wiring for the selected source.
- Reading timer units as timing guarantees. Microseconds are the timer API’s units; effective resolution depends on the RTC slow clock.
- Expecting Wi-Fi or Bluetooth to stay connected. Those peripherals power down during deep sleep, so complete required communications first.
- Reusing a sleep configuration without checking enabled sources. Wake sources remain enabled unless explicitly disabled; verify compatibility when combining them or changing strategy.
Reference
Espressif Systems, Sleep Modes – ESP32 – ESP-IDF Programming Guide v6.1 documentation, accessed October 4, 2026.
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