ESP32 Deep Sleep modes with Arduino IDE

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ESP32 comes with a dual-core processor. The dual-core processing provides efficiency in terms of performance as well as power consumption. In this post, we’ll explore how to access both cores on the ESP32 and compare the performance between single-core and dual-core operations.

Table of Content

ESP32 Power Modes

ESP32 has Five Power Modes:

• Active Mode
• Mode-Sleep Mode
• Light-Sleep Mode
• Deep-Sleep Mode
• Hibernation Mode

Power Mode	CPU	Wi-Fi/Bluetooth	RTC Memory & Peripherals	ULP	Power Consumption
Active Mode	ON	ON	ON	ON	Refer [RF Modes]
Modem-Sleep Mode	ON	OFF	ON	ON	20 mA to 68 mA
Light-Sleep Mode	PAUSE	OFF	ON	ON	0.8 mA
Deep-Sleep Mode	OFF	OFF	ON	ON	10 uA to 150 uA
Hibernation Mode	OFF	OFF	RTC Memory – OFF RTC Timer – ON (Slow clock 8 MHz) RTC GPIOs – ON	OFF	5 uA
Power Off	OFF	OFF	OFF	OFF	1 uA

Please find power consumption for various RF modes in ESP32:

RF Mode	Min	Typ	Max	Unit
Transmit 802.11b, DSSS 1 Mbps, POUT = +19.5 dBm	–	240	–	mA
Transmit 802.11g, OFDM 54 Mbps, POUT = +16 dBm	–	190	–	mA
Transmit 802.11n, OFDM MCS7, POUT = +14 dBm	–	180	–	mA
Receive 802.11b/g/n	–	95 to 100	–	mA
Transmit BT/BLE, POUT = 0 dBm	–	130	–	mA
Receive BT/BLE	–	95 to 100	–	mA

Why Sleep Modes?

Imagine you have an ESP32 Smartwatch. Let’s assume we have a battery of 500 mAH and other sensors, display, and modules consume negligible power. Let’s compare the battery backup of the watch in active vs sleep mode. Let’s assume our device is 90% of the time is in Deep-Sleep Mode and 10 % of the time in Active Mode.

battery backup = battery capacity (mAH) / current consumption

battery backup_{(Active Mode)} = 500 (mAH) / 240 mA = 2.1 Hours
battery backup_(Deep-Sleep) = 500 (mAH) / {(150*0.9 uA)+(240*0.1 mA)} = 21 Hours

From the battery life calculation, you can clearly see that the watch will have 10x more battery backup. You can still increase the battery backup by putting the ESP32 into Hibernation mode and increasing the sleep duration.

Putting ESP32 in different Power Modes?

The function esp_deep_sleep_start(void) puts ESP32 in Deep-Sleep Mode. However, you need to define the wakeup source before putting ESP32 into sleep mode.

esp_deep_sleep_start(void);

Wakeup Sources

#define TIME_TO_SLEEP  5

void setup() {
  Serial.begin(115200);
  delay(1000);
  Serial.println(esp_sleep_get_wakeup_cause());
  
  Serial.println("ESP32 is going to sleep for ...");
  // Enable timer wakeup
  esp_sleep_enable_timer_wakeup(TIME_TO_SLEEP * 1000000); // Convert to microseconds

  // Start deep sleep
  Serial.println("ESP32 sleeping now");
  Serial.flush(); 
  esp_deep_sleep_start();
  Serial.println("ESP32 sleeping now")
}

void loop() {
   Serial.println("Inside loop() function")
}