ESP32 practical power saving: deep sleep and hibernation – 3

by Renzo Mischianti · Published 15 March 2021 · Updated 27 January 2022

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The most common power-saving mode for ESP32 is deep sleep, and here we will see what deep sleep is and the difference between hibernate variants.

ESP32 practical power saving deep sleep and hibernation — ESP32 practical power-saving deep sleep and hibernation

A hibernation-like sleep modem is a logical definition that you have to manage. There is no specific command, it is “activated” by applying a certain logic, and since this mode offers excellent advantages, it can push you to change the logic of your code.

In deep sleep mode, CPUs, most of the RAM, and all the digital peripherals, managed from the clock of the Advanced Peripheral Bus (APB_CLK), are powered off. The only parts of the chip which can still be powered on are real-time clock (RTC) controller, RTC peripherals, Ultra-Low Power (ULP) coprocessor, and RTC memories (slow and fast).

Function Block diagram Espressif esp32 Wi-Fi Bluetooth Microcontroller

In this table from the datasheet of esp32, there is information about group sleep mode.

Power mode	Description			Power consumption
Active (RF working)	Wi-Fi Tx packet			78 mA ~ 90 mA without communication For TX RX more info in the next table
	Wi-Fi/BT Tx packet
	Wi-Fi/BT Rx and listening
Modem-sleep	The CPU is powered on.	240 MHz *	Dual-core chip(s)	30 mA ~ 68 mA
			Single-core chip(s)	N/A
		160 MHz *	Dual-core chip(s)	27 mA ~ 44 mA
			Single-core chip(s)	27 mA ~ 34 mA
		Normal speed: 80 MHz	Dual-core chip(s)	20 mA ~ 31 mA
			Single-core chip(s)	20 mA ~ 25 mA
Light-sleep	–			0.8 mA
Deep-sleep	The ULP co-processor is powered on.			150 µA 100 µA @1% duty 10 µA
	ULP sensor-monitored pattern
	RTC timer + RTC memory
Hibernation	RTC timer only			5 µA
Power off	CHIP_PU is set to low level, the chip is powered off.			1 µA

Deep sleep

Deep sleep is the most efficient way to put your device to sleep. Still, there is a big difference from light sleep, making it less usable. The state is cleared, so if you had set a variable when restarting your device, the variable is reset, and the program restarted from the initial setup.

But you must pay attention; in my block diagram, I give color on peripheral because the only real difference from hibernate is what functional unit must remain active, here what write Espressif.

RTC IO module contains logic to trigger wakeup when one of RTC GPIOs is set to a predefined logic level. RTC IO is part of RTC peripherals power domain, so RTC peripherals will be kept powered on during deep sleep if this wakeup source is requested.
From Espressif documentation

So if we are going to use an external wake-up source, we will use a deep sleep; if we use nothing or only the RTC, we have a hibernation.

So here is a simple sketch to test deep sleep.

/*
 *  ESP32
 *  DEEP Sleep and wake up
 *  by Mischianti Renzo <https://mischianti.org>
 *
 *  https://mischianti.org/esp32-practical-power-saving-deep-sleep-and-hibernation-3/
 *
 */

#include <WiFi.h>
#include <BluetoothSerial.h>
#include "driver/adc.h"
#include <esp_bt.h>
#include <esp_wifi.h>
#include <esp_sleep.h>

#define STA_SSID "<YOUR-SSID>"
#define STA_PASS "<YOUR-PASSWD>"

BluetoothSerial SerialBT;

int variable = 0;

void setup() {
	Serial2.begin(115200);

	while(!Serial2){delay(500);}

  	SerialBT.begin("ESP32test"); //Bluetooth device name
	SerialBT.println("START BT");

	Serial2.println("START WIFI");
	WiFi.begin(STA_SSID, STA_PASS);

    while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial2.print(".");
    }

    Serial2.println("");
    Serial2.println("WiFi connected");
    Serial2.println("IP address: ");
    Serial2.println(WiFi.localIP());

    delay(1000);

    Serial2.print("Initial Variable value = ");
    Serial2.println(variable);

    variable += 10;

    Serial2.print("Variable updated = ");
    Serial2.println(variable);

    Serial2.println();
    Serial2.println("DEEP SLEEP ENABLED FOR 5secs");
    delay(100);

    esp_sleep_enable_timer_wakeup(5 * 1000 * 1000);
    // Pay attention to this command, with this wake up source
    // your device can't go to hibernate mode
    // but only deep sleep
    esp_sleep_enable_ext0_wakeup(GPIO_NUM_33,1);

    esp_deep_sleep_start();

    Serial2.println();
    Serial2.println("DEEP SLEEP WAKE UP");

    Serial2.print("Variable = ");
    Serial2.println(variable);
}

void loop() {

}

void disableWiFi(){
    adc_power_off();
	WiFi.disconnect(true);  // Disconnect from the network
	WiFi.mode(WIFI_OFF);    // Switch WiFi off

	Serial2.println("");
	Serial2.println("WiFi disconnected!");
}
void enableWiFi(){
	adc_power_on();
	WiFi.disconnect(false);  // Reconnect the network
	WiFi.mode(WIFI_STA);    // Switch WiFi off

	Serial2.println("START WIFI");
	WiFi.begin(STA_SSID, STA_PASS);

    while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial2.print(".");
    }

    Serial2.println("");
    Serial2.println("WiFi connected");
    Serial2.println("IP address: ");
    Serial2.println(WiFi.localIP());
}
void disableBluetooth(){
	btStop();
	esp_bt_controller_disable();
	delay(1000);
	Serial2.println("BT STOP");
}

When launching the sketch, we denote the first difference from light sleep, the variable state is not preserved in deep sleep mode, and the program flow restart from setup().

As you can see, the variable’s value is 0, and it is reset every time. And every time the esp32 comes out of deep sleep, it restarts from the initial. setup().

Now we are going to test this sketch with our three devices.

DOIT DEV KIT v1

For more information on the device, refer to “DOIT ESP32 DEV KIT v1 high resolution pinout and specs“.

Here is the connection schema we used.

Power the esp32 to the 5v pin and GND pin with an external power supply and disconnect the USB. To log, we use the Serial2 port, but if you want to use the Serial port, you must only move the FTDI converter to the TX pin instead TX2 pin; you can’t use USB because it powers the device, and the multimeter gets the wrong amperage.

Data

Again the result is not good; this device in hibernate consumes 12.19mA, very, very, very far from the 150µA declared from Espressif.

As happened for light sleep at first, I was depressed, but from the experience of light sleep, I understand that the device I use is not designed for production; in a dev board, there is a lot of other components that can change the result, like LEDs, voltage regulators, etc.

I try to do the same test with two famous boards vendors that have devices with battery management and other features, not only for development.

TTGO T8

First, I want to try a TTGO, one of the most famous productor of this kind of device, with many variants; I use one of its better products, the TTGO T8.

The power source at 5v from the specified pin gives a lousy result of 9.63mA. Still, when powered only with a battery, the board excludes some functional units like led, voltage regulator, etc., so the same test with battery power reaches 4.56mA more likely result.

WeMos LOLIN32

For more information on the device, refer to “ESP32 WeMos LOLIN32 high resolution pinout and specs“.

The wiring diagram

ESP32 WeMos LOLIN32 powered to 5V and Serial2 to debug amperage multimerter check — ESP32 WeMos LOLIN32 powered to 5V and Serial2 to debug amperage multimeter check

Wiring diagram with battery.

ESP32 WeMos LOLIN32 powered with battery and Serial2 to debug amperage multimerter check

Then the WeMos LOLIN32; I love WeMos as a manufacturer, I believe I have a good set of devices, and these are very versatile with various sizes.

The result with the power source at 5v from the specified pin gives a better result, 2.92mA, and the board, when powered only with the battery, reaches 1.81mA.

Device	Mode	Power
DOIT DEV KIT v1	Power to VIN pin	12.19mA
TTGO T8	Power to 5V pin	9.63mA
	Power via Battery	4.56mA
WeMos LOLIN32	Power via 5V pin	2.92mA
	Power via Battery	1.81mA

Hibernation

Hibernation is similar to deep sleep, but you have to give up some wake-up possibilities like external sources.

I create a simple sketch to test the hibernation performance

/*
 *  ESP32
 *  DEEP Sleep and wake up
 *  by Mischianti Renzo <https://mischianti.org>
 *
 *  https://mischianti.org/esp32-practical-power-saving-deep-sleep-and-hibernation-3/
 *
 */

#include <WiFi.h>
#include <BluetoothSerial.h>
#include "driver/adc.h"
#include <esp_bt.h>
#include <esp_wifi.h>
#include <esp_sleep.h>

#define STA_SSID "<YOUR-SSID>"
#define STA_PASS "<YOUR-PASSWD>"

BluetoothSerial SerialBT;

int variable = 0;

void setup() {
	Serial2.begin(115200);

	while(!Serial2){delay(500);}

  	SerialBT.begin("ESP32test"); //Bluetooth device name
	SerialBT.println("START BT");

	Serial2.println("START WIFI");
	WiFi.begin(STA_SSID, STA_PASS);

    while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial2.print(".");
    }

    Serial2.println("");
    Serial2.println("WiFi connected");
    Serial2.println("IP address: ");
    Serial2.println(WiFi.localIP());

    delay(1000);

    Serial2.print("Initial Variable value = ");
    Serial2.println(variable);

    variable += 10;

    Serial2.print("Variable updated = ");
    Serial2.println(variable);

    Serial2.println();
    Serial2.println("DEEP SLEEP ENABLED FOR 5secs");
    delay(100);

    esp_sleep_enable_timer_wakeup(5 * 1000 * 1000);
    esp_deep_sleep_start();

    Serial2.println();
    Serial2.println("DEEP SLEEP WAKE UP");

    Serial2.print("Variable = ");
    Serial2.println(variable);
}

void loop() {

}

void disableWiFi(){
    adc_power_off();
	WiFi.disconnect(true);  // Disconnect from the network
	WiFi.mode(WIFI_OFF);    // Switch WiFi off

	Serial2.println("");
	Serial2.println("WiFi disconnected!");
}
void enableWiFi(){
	adc_power_on();
	WiFi.disconnect(false);  // Reconnect the network
	WiFi.mode(WIFI_STA);    // Switch WiFi off

	Serial2.println("START WIFI");
	WiFi.begin(STA_SSID, STA_PASS);

    while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial2.print(".");
    }

    Serial2.println("");
    Serial2.println("WiFi connected");
    Serial2.println("IP address: ");
    Serial2.println(WiFi.localIP());
}
void disableBluetooth(){
	btStop();
	esp_bt_controller_disable();
	delay(1000);
	Serial2.println("BT STOP");
}

To put the devices in hibernation instead of Deep sleep, I remove the external wake-up source ext0. Remember ext0 put in deep sleep, but ext1 prevent the use of deep sleep.