ESP32 practical power saving: deep sleep and hibernation – 3

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.

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).

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

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

Wiring diagram with battery.

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.

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.

DOIT DEV KIT v1

The hibernation has better results concerning deep sleep, and DEV KIT v1 consumes 3.46mA, but It’s very far from the 5µA declared from Espressif.

I try to do the same test with two famous boards vendor devices with battery management and other features, not only for dev.

TTGO T8

The result with the power source at 5v from the specified pin gives a bad result of 7.95mA, but the same test with battery power reach 3.33mA, relatively better than the first result and then DOIT DEV KIT v1.

WeMos LOLIN32

The result with the power source at 5v from the specified pin gives a better result of 1.26mA, but the board, when powered only with a battery, reaches 160µA, which is a perfect result.

Results

The data is unequivocal, and the DOIT DEV KIT v1 is the loser and the LOLIN32 winner. TTGO has the highest price cannot be considered up to par.

Thanks

1. ESP32: pinout, specs and Arduino IDE configuration
2. ESP32: integrated SPIFFS Filesystem
3. ESP32: manage multiple Serial and logging
4. ESP32 practical power saving
   1. ESP32 practical power saving: manage WiFi and CPU
   2. ESP32 practical power saving: modem and light sleep
   3. ESP32 practical power saving: deep sleep and hibernation
   4. ESP32 practical power saving: preserve data, timer and touch wake up
   5. ESP32 practical power saving: external and ULP wake up
   6. ESP32 practical power saving: UART and GPIO wake up
5. ESP32: integrated LittleFS FileSystem
6. ESP32: integrated FFat (Fat/exFAT) FileSystem
7. ESP32-wroom-32
   1. ESP32-wroom-32: flash, pinout, specs and IDE configuration
8. ESP32-CAM
   1. ESP32-CAM: pinout, specs and Arduino IDE configuration
   2. ESP32-CAM: upgrade CamerWebServer with flash features
9. ESP32: use ethernet w5500 with plain (HTTP) and SSL (HTTPS)
10. ESP32: use ethernet enc28j60 with plain (HTTP) and SSL (HTTPS)
11. How to use SD card with esp32
12. esp32 and esp8266: FAT filesystem on external SPI flash memory

13. Firmware and OTA update management
    1. Firmware management
       1. ESP32: flash compiled firmware (.bin)
       2. ESP32: flash compiled firmware and filesystem (.bin) with GUI tools
    2. OTA update with Arduino IDE
       1. ESP32 OTA update with Arduino IDE: filesystem, firmware, and password
    3. OTA update with Web Browser
       1. ESP32 OTA update with Web Browser: firmware, filesystem, and authentication
       2. ESP32 OTA update with Web Browser: upload in HTTPS (SSL/TLS) with self-signed certificate
       3. ESP32 OTA update with Web Browser: custom web interface
    4. Self OTA uptate from HTTP server
       1. ESP32 self OTA update firmware from the server
       2. ESP32 self OTA update firmware from the server with version check
       3. ESP32 self-OTA update in HTTPS (SSL/TLS) with trusted self-signed certificate
    5. Non-standard Firmware update
       1. ESP32 firmware and filesystem update from SD card
       2. ESP32 firmware and filesystem update with FTP client

14. Integrating LAN8720 with ESP32 for Ethernet Connectivity with plain (HTTP) and SSL (HTTPS)
15. Connecting the EByte E70 to ESP32 c3/s3 devices and a simple sketch example
16. ESP32-C3: pinout, specs and Arduino IDE configuration
17. Integrating W5500 with ESP32 Using Core 3: Native Ethernet Protocol Support with SSL and Other Features
18. Integrating LAN8720 with ESP32 Using Core 3: Native Ethernet Protocol Support with SSL and Other Features