Wake-up from sleep with interrupt in Arduino - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of using interrupts to wake up an Arduino from sleep mode?

Interrupts allow the Arduino to wake up immediately when a specific event occurs, saving power by sleeping until needed.

beginner

Which Arduino function is used to put the microcontroller into sleep mode?

The sleep_mode() function from the avr/sleep.h library is used to put the Arduino into sleep mode.

intermediate

How do you attach an interrupt to a pin to wake the Arduino from sleep?

Use attachInterrupt(digitalPinToInterrupt(pin), ISR, mode) where ISR is the interrupt service routine and mode defines the trigger condition (e.g., RISING).

intermediate

What must you do inside the Interrupt Service Routine (ISR) to wake the Arduino from sleep?

The ISR should be short and can set a flag or simply return; the interrupt itself wakes the Arduino from sleep automatically.

advanced

Why is it important to disable ADC and other peripherals before sleeping?

Disabling ADC and unused peripherals reduces power consumption, making sleep mode more effective.

Which library is commonly used to control sleep modes on Arduino?

A Wire.h

B avr/sleep.h

C SPI.h

D EEPROM.h

The avr/sleep.h library provides functions to manage sleep modes on Arduino.

What does attachInterrupt(digitalPinToInterrupt(pin), ISR, RISING) do?

A Sets an interrupt on the pin triggered when the signal rises

B Puts the Arduino to sleep

C Disables the interrupt on the pin

D Reads the digital value of the pin

It attaches an interrupt to the specified pin that triggers the ISR when the signal changes from LOW to HIGH.

What happens when an interrupt occurs while Arduino is sleeping?

A Arduino shuts down

B Arduino stays asleep

C Arduino resets

D Arduino wakes up and runs the ISR

An interrupt wakes the Arduino from sleep and executes the interrupt service routine.

Which of these is NOT a valid interrupt trigger mode?

A STABLE

B FALLING

C RISING

D CHANGE

STABLE is not a valid interrupt trigger mode; valid modes include RISING, FALLING, and CHANGE.

Why should the ISR be kept short when waking from sleep?

A To disable interrupts

B To use more memory

C To quickly return control and avoid delays

D To put Arduino back to sleep

Short ISRs ensure the Arduino resumes normal operation quickly without blocking other processes.

Explain how to set up an Arduino to wake up from sleep using an external interrupt.

Think about the steps from preparing sleep to waking up with a button press.

Describe why using interrupts to wake from sleep is better for power saving than polling.

Compare continuous checking vs waiting quietly.

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()