Wake-up from sleep with interrupt in Arduino - Mini Project: Build & Apply

Wake-up from Sleep with Interrupt

📖 Scenario: You are building a simple Arduino project that saves power by going to sleep and wakes up only when a button is pressed. This is useful for battery-powered devices that need to stay off most of the time and react only to user input.

🎯 Goal: Create an Arduino program that puts the board to sleep and wakes it up using an external interrupt triggered by a button press.

📋 What You'll Learn

Use the LowPower library to manage sleep mode

Set up a button connected to pin 2 to trigger an interrupt

Use an interrupt service routine (ISR) to wake the Arduino

Print a message to the Serial Monitor when the Arduino wakes up

💡 Why This Matters

🌍 Real World

Battery-powered devices like remote sensors or wearable gadgets often need to save power by sleeping and waking only when needed.

💼 Career

Understanding interrupts and power management is essential for embedded systems engineers and IoT developers to build efficient, low-power devices.

1

Setup button input and Serial communication

Write code to set up the button on pin 2 as an input with an internal pull-up resistor. Also, start the Serial communication at 9600 baud in the setup() function.

Arduino

void setup() {
  // Set pin 2 as input with internal pull-up resistor
  // Start Serial communication at 9600 baud
  // Your code here
}

void loop() {
  // Empty loop for now
}

Hint

Use pinMode to set the button pin as input with pull-up. Use Serial.begin(9600) to start serial communication.

2

Configure interrupt to wake from sleep

Add code to attach an interrupt on pin 2 that triggers on a falling edge. Create an empty interrupt service routine called wakeUp that will be called when the interrupt occurs.

Arduino

void setup() {
  pinMode(2, INPUT_PULLUP);
  Serial.begin(9600);
  // Attach interrupt on pin 2 for falling edge to wakeUp
  // Your code here
}

void loop() {
  // Empty loop for now
}

// Define the wakeUp ISR
void wakeUp() {
  // Your code here
}

Hint

Use attachInterrupt(digitalPinToInterrupt(2), wakeUp, FALLING) to set the interrupt. The ISR wakeUp should be empty or very short.

3

Put Arduino to sleep and wake on interrupt

Include the LowPower.h library at the top. In the loop() function, put the Arduino to sleep using LowPower.powerDown(SLEEP_FOREVER, ADC_OFF, BOD_OFF). The Arduino will wake up when the interrupt triggers.

Arduino

#include 

void setup() {
  pinMode(2, INPUT_PULLUP);
  Serial.begin(9600);
  attachInterrupt(digitalPinToInterrupt(2), wakeUp, FALLING);
}

void loop() {
  // Put Arduino to sleep here
  // Your code here
}

void wakeUp() {
  // ISR must be empty or minimal
}

Hint

Include the LowPower library and call LowPower.powerDown(SLEEP_FOREVER, ADC_OFF, BOD_OFF) inside loop() to sleep indefinitely until interrupt.

4

Print message after waking up

Add a Serial.println("Woke up!") statement right after the sleep call in the loop() function to show when the Arduino wakes up.

Arduino

#include 

void setup() {
  pinMode(2, INPUT_PULLUP);
  Serial.begin(9600);
  attachInterrupt(digitalPinToInterrupt(2), wakeUp, FALLING);
}

void loop() {
  LowPower.powerDown(SLEEP_FOREVER, ADC_OFF, BOD_OFF);
  // Print "Woke up!" after waking up
  // Your code here
}

void wakeUp() {
  // ISR must be empty or minimal
}

Hint

Use Serial.println("Woke up!") after the sleep call to show the wake-up message.

Practice

1. What is the main purpose of using an interrupt to wake an Arduino from sleep mode?

easy

A. To allow the Arduino to respond immediately to an external event while saving power

B. To make the Arduino run faster during normal operation

C. To reset the Arduino automatically after a delay

D. To increase the Arduino's memory capacity

Solution

1. Step 1: Understand sleep mode purpose

   Arduino sleep mode reduces power consumption by stopping most activities.

2. Step 2: Role of interrupts in sleep mode

   Interrupts allow the Arduino to wake up immediately when an external event occurs, saving power while staying responsive.

3. Final Answer:

   To allow the Arduino to respond immediately to an external event while saving power -> Option A

4. Quick Check:

   Interrupt wakes Arduino from sleep to save power [OK]

Hint: Interrupts wake Arduino instantly during sleep to save power [OK]

Common Mistakes:

• Thinking interrupts speed up normal running
• Confusing interrupts with reset functions
• Believing interrupts increase memory

2. Which of the following is the correct way to attach an interrupt to pin 2 that triggers on a RISING signal?

easy

A. attachInterrupt(2, ISR, FALLING);

B. attachInterrupt(digitalPinToInterrupt(2), ISR, RISING);

C. attachInterrupt(digitalPinToInterrupt(3), ISR, CHANGE);

D. attachInterrupt(2, ISR, LOW);

Solution

1. Step 1: Use digitalPinToInterrupt() for pin mapping

   Pin 2 must be converted using digitalPinToInterrupt(2) for portability.

2. Step 2: Set correct trigger mode

   RISING triggers interrupt when signal goes from LOW to HIGH.

3. Final Answer:

   attachInterrupt(digitalPinToInterrupt(2), ISR, RISING); -> Option B

4. Quick Check:

   Correct pin and RISING trigger = attachInterrupt(digitalPinToInterrupt(2), ISR, RISING); [OK]

Hint: Always use digitalPinToInterrupt(pin) with correct trigger [OK]

Common Mistakes:

• Using pin number directly without digitalPinToInterrupt()
• Choosing wrong trigger mode like FALLING or LOW
• Attaching interrupt to wrong pin number

3. What will be the output on the serial monitor after running this code if a button connected to pin 2 is pressed once?

void ISR() {
  Serial.println("Woke up!");
}

void setup() {
  Serial.begin(9600);
  attachInterrupt(digitalPinToInterrupt(2), ISR, RISING);
  sleep_enable();
  sleep_mode();
  Serial.println("Sleeping...");
}

void loop() {
  // Empty loop
}

medium

A. No output at all

B. Woke up!\nSleeping...

C. Sleeping... (no further output)

D. Sleeping...\nWoke up!

Solution

1. Step 1: Analyze print locations

   "Sleeping..." prints after sleep_mode(), so it executes after waking up.

2. Step 2: ISR execution order

   ISR prints "Woke up!" immediately upon interrupt, before resuming code after sleep_mode().

3. Final Answer:

   Sleeping...\nWoke up! -> Option D

4. Quick Check:

   Code after sleep_mode() runs after ISR, so output order is Sleeping... then Woke up! [OK]

Hint: ISR runs immediately on interrupt, but code after sleep_mode() runs after ISR [OK]

Common Mistakes:

• Thinking "Sleeping..." prints before sleep
• Believing no output after wake
• Expecting Sleeping... before ISR

4. Identify the error in this code snippet that tries to wake Arduino from sleep on pin 3 interrupt:

void ISR() {
  // Empty ISR
}

void setup() {
  attachInterrupt(3, ISR, FALLING);
  sleep_enable();
  sleep_mode();
}

void loop() {
  // Empty
}

medium

A. attachInterrupt() uses pin number directly instead of digitalPinToInterrupt()

B. ISR function should not be empty

C. sleep_mode() should be called inside loop()

D. sleep_enable() must be called after sleep_mode()

Solution

1. Step 1: Check attachInterrupt() usage

   Pin number must be converted with digitalPinToInterrupt(pin) for correct interrupt mapping.

2. Step 2: Validate other parts

   Empty ISR is allowed; sleep_mode() can be in setup; sleep_enable() must be before sleep_mode().

3. Final Answer:

   attachInterrupt() uses pin number directly instead of digitalPinToInterrupt() -> Option A

4. Quick Check:

   Pin mapping requires digitalPinToInterrupt() [OK]

Hint: Always convert pin with digitalPinToInterrupt() in attachInterrupt() [OK]

Common Mistakes:

• Not using digitalPinToInterrupt() for pin mapping
• Thinking ISR must have code
• Misplacing sleep_enable() call

5. You want to put your Arduino to sleep and wake it up only when a button connected to pin 4 is pressed. Which sequence correctly implements this behavior?

hard

A. attachInterrupt(digitalPinToInterrupt(4), wakeISR, LOW); sleep_enable(); sleep_mode();

B. attachInterrupt(4, wakeISR, RISING); sleep_disable(); sleep_mode();

C. attachInterrupt(digitalPinToInterrupt(4), wakeISR, FALLING); sleep_enable(); sleep_mode();

D. attachInterrupt(digitalPinToInterrupt(4), wakeISR, CHANGE); sleep_enable(); sleep_disable();

Solution

1. Step 1: Attach interrupt correctly

   Use digitalPinToInterrupt(4) and FALLING trigger for button press (assuming active LOW button).

2. Step 2: Enable sleep and enter sleep mode

   Call sleep_enable() before sleep_mode() to allow waking on interrupt.

3. Final Answer:

   attachInterrupt(digitalPinToInterrupt(4), wakeISR, FALLING); sleep_enable(); sleep_mode(); -> Option C

4. Quick Check:

   Correct pin, trigger, and sleep calls = attachInterrupt(digitalPinToInterrupt(4), wakeISR, FALLING); sleep_enable(); sleep_mode(); [OK]

Hint: Use digitalPinToInterrupt() with sleep_enable() before sleep_mode() [OK]

Common Mistakes:

• Using sleep_disable() before sleep_mode()
• Wrong trigger mode like LOW or CHANGE for button press
• Not enabling sleep before entering sleep_mode()