In the realm of electronics and embedded systems, power efficiency is a critical concern, especially for battery-operated devices. Sleep modes in microcontrollers, like those used in Arduino boards, offer a way to significantly reduce power consumption by putting the microcontroller into a low-power state when it's not actively performing tasks. This article delves into the various sleep modes available in Arduino, their importance, and how to implement them effectively in your projects.

Project: In this example project, we will create a simple temperature monitoring system using an Arduino board and a temperature sensor. The system will periodically wake up from sleep mode, read the temperature, and then return to sleep mode to conserve power. The objective is to demonstrate how to utilize sleep modes to extend the battery life of the project.

Components List:

• Arduino Uno (1)
• DHT11 Temperature and Humidity Sensor (1)
• Resistor 10kΩ (1)
• Breadboard (1)
• Jumper Wires (as needed)
• USB Cable (1)

Examples:

// Include necessary libraries
#include <avr/sleep.h>
#include <avr/wdt.h>
#include <DHT.h>

// Define pin for DHT11 sensor
#define DHTPIN 2
#define DHTTYPE DHT11

// Create DHT object
DHT dht(DHTPIN, DHTTYPE);

// Function to configure watchdog timer for sleep
void setup_watchdog(int prescalar) {
  byte bb;
  if (prescalar > 9 ) prescalar = 9; // Limit prescalar to 9
  bb = prescalar & 7; // Set lower three bits
  if (prescalar > 7) bb |= (1<<5); // Set bit 5 if prescalar > 7
  bb |= (1<<WDCE) | (1<<WDE); // Enable configuration change
  MCUSR &= ~(1<<WDRF); // Clear WDRF
  WDTCSR |= (1<<WDCE) | (1<<WDE); // Start timed sequence
  WDTCSR = bb; // Set new watchdog timeout value
  WDTCSR |= _BV(WDIE); // Enable watchdog interrupt
}

// Watchdog interrupt service routine
ISR(WDT_vect) {
  // Do nothing, just wake up from sleep
}

void setup() {
  // Initialize serial communication
  Serial.begin(9600);
  // Initialize DHT sensor
  dht.begin();
  // Setup watchdog timer with 8s timeout
  setup_watchdog(6);
}

void loop() {
  // Read temperature from DHT11 sensor
  float temperature = dht.readTemperature();
  // Print temperature to serial monitor
  Serial.print("Temperature: ");
  Serial.print(temperature);
  Serial.println(" *C");

  // Put the Arduino to sleep
  set_sleep_mode(SLEEP_MODE_PWR_DOWN); // Set sleep mode to power down
  sleep_enable(); // Enable sleep mode
  sleep_mode(); // Go to sleep

  // The program continues here after waking up
  sleep_disable(); // Disable sleep mode
}

Explanation:

1. Including Libraries: We include necessary libraries for sleep modes and the DHT sensor.
2. Defining Pins and Objects: We define the pin for the DHT11 sensor and create a DHT object.
3. Watchdog Timer Setup: The setup_watchdog function configures the watchdog timer to wake up the Arduino from sleep mode after a specified interval.
4. Interrupt Service Routine: The ISR for the watchdog timer is defined to handle the wake-up event.
5. Setup Function: Initializes serial communication, the DHT sensor, and sets up the watchdog timer.
6. Loop Function: Reads the temperature, prints it to the serial monitor, and then puts the Arduino to sleep. The watchdog timer wakes it up after the specified interval, and the loop continues.