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Deep sleep

This tutorial will show how to put an ESP32 into deep sleep, and how to wake it up again.

If you are using Toit's fleet management, then you don't need to worry about deep sleep. Artemis (the installed container of the fleet management system) automatically puts the device into deep sleep when it is not running any programs.

Prerequisites

We assume that you have set up your development environment as described in the IDE tutorial.

We also assume that you have flashed your device with Jaguar and that you are familiar with running Toit programs on it. If not, have a look at the Hello world tutorial.

While not necessary, we recommend to have done the LED, Button and Touch button tutorials before this one.

Putting to sleep

The ESP32 can be put into deep sleep by calling the deep-sleep method of the esp32 library. This method takes a single argument, which is the duration of the sleep.

Write the following sleep.toit program and run it with Jaguar.

import esp32

main:
  esp32.deep-sleep (Duration --s=2)

This program will let the ESP32 sleep for 2 seconds, and then wake up again.

If a program is installed as a container and starts at boot, then an early deep-sleep call could make the device unresponsive.

If your are using Jaguar for development, but Jaguar doesn't have the time to start before the device goes back to sleep then you can't update the program anymore. In this case you have to flash the device again.

You can avoid this by either ensuring that the device is awake for a certain time, or by not going to sleep if a certain pin is pulled low.

For example:

import gpio
import esp32

main:
  sleep-pin := gpio.Pin --input 33 --pull-up
  if sleep-pin.get != 0:
    // Not pulled low. Go to sleep.
    esp32.deep-sleep (Duration --s=2)

This way you always have a way to recover from such a scenario.

Wake up from external pin

The ESP32 can be woken up from deep sleep if certain pins are low or high.

Setup

Connect pin 32 to ground (optionally with a 330Ω resistor in between).

Code

Edit your sleep.toit program to the following:

import esp32

main:
  // Enable wakeup if pin 32 goes high.
  pin-mask := 1 << 32
  on-any-high := true
  esp32.enable-external-wakeup pin-mask on-any-high
  esp32.deep-sleep (Duration --m=3)

Run it, and then remove the connection between pin 32 and ground. Without any pull-down resistor the pin is floating and thus measures mostly random values. You are likely to see the ESP32 wake up almost immediately. If not, try touching the pin with your finger or even connecting the pin to 3V3.

If you have a button (especially the ones with integrated pull-down resistors) you can also use it to wake up the ESP32.

Wake up from touch

The ESP32 can also be woken up with the touch sensor.

Setup

Connect a male-male jumper wire to pin 32. Keep one end of the wire free. We will use this end as touch button.

Code

Edit your sleep.toit program to the following and run it with Jaguar. If necessary change the threshold value. See the Touch button tutorial for more information about the touch sensor.

import esp32
import gpio
import gpio.touch as gpio

main:
  pin := gpio.Pin 32
  touch := gpio.Touch pin
  touch.threshold = 800
  esp32.enable-touchpad-wakeup
  esp32.deep-sleep (Duration --m=3)

The ESP32 will go to sleep for three minutes, or wake up if it registers a touch on pin 32.

Power consumption

When the ESP32 is in deep sleep it only consumes about 10µA. However, this assumes that no other components are drawing any power. There are significant differences between different ESP32 boards.

For example the FireBeetle ESP32 uses only 10µA when in deep sleep, the Olimex ESP32-DevKit-LiPo around 65µA, and the ESP32-DevKitC up to 9mA.