Arduino sleep modes - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to put the Arduino into sleep mode.

Arduino

#include <avr/sleep.h>

void setup() {
  Serial.begin(9600);
  set_sleep_mode([1]);
  sleep_enable();
  sleep_cpu();
}

void loop() {
  // Nothing here
}

Drag options to blanks, or click blank then click option'

ASLEEP_MODE_IDLE

BSLEEP_MODE_PWR_DOWN

CSLEEP_MODE_ADC

DSLEEP_MODE_STANDBY

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a lighter sleep mode that doesn't save much power.

The SLEEP_MODE_PWR_DOWN mode puts the Arduino into the deepest sleep, saving the most power.

2fill in blank

medium

Complete the code to disable sleep mode after waking up.

Arduino

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

void setup() {
  attachInterrupt(digitalPinToInterrupt(2), wakeUp, [1]);
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  sleep_enable();
  sleep_cpu();
}

void loop() {
  // Sleep until interrupt
}

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ALOW

BCHANGE

CRISING

DFALLING

Attempts:

3 left

💡 Hint

Common Mistakes

Using LOW, which triggers continuously while the pin is held low.

The interrupt triggers on a rising edge signal, waking the Arduino from sleep.

3fill in blank

hard

Fix the error in the code to correctly enter sleep mode.

Arduino

#include <avr/sleep.h>

void setup() {
  Serial.begin(9600);
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  [1]();
  sleep_cpu();
}

void loop() {
  // Sleep here
}

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Asleep_enable

Bsleep_mode

Csleep_disable

Dsleep_set

Attempts:

3 left

💡 Hint

Common Mistakes

Calling sleep_disable() instead of sleep_enable().

You must call sleep_enable() before sleep_cpu() to activate sleep mode.

4fill in blank

hard

Fill both blanks to create a dictionary of sleep modes and their descriptions.

Arduino

const char* sleepModes[] = {"[1]", "[2]"};

void setup() {
  Serial.begin(9600);
  Serial.println(sleepModes[0]);
  Serial.println(sleepModes[1]);
}

void loop() {}

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ASLEEP_MODE_IDLE

BSLEEP_MODE_PWR_SAVE

CIdle mode

DPower save mode

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing mode names with descriptions incorrectly.

The array holds the mode name and its description. Here, SLEEP_MODE_IDLE and "Idle mode" are paired.

5fill in blank

hard

Fill all three blanks to create a function that sets sleep mode and enters sleep.

Arduino

void enterSleepMode([1] mode) {
  set_sleep_mode([2]);
  [3]();
  sleep_cpu();
}

void setup() {
  Serial.begin(9600);
  enterSleepMode(SLEEP_MODE_PWR_DOWN);
}

void loop() {}

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Auint8_t

Bmode

Csleep_enable

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter type or forgetting to enable sleep.

The function takes an integer mode, sets it as the sleep mode, enables sleep, then enters sleep.

Practice

1. Which Arduino function is used to set the type of sleep mode before entering sleep?

easy

A. set_sleep_mode()

B. sleep_cpu()

C. attachInterrupt()

D. delay()

Solution

1. Step 1: Understand sleep mode setup

   The function set_sleep_mode() is used to choose which sleep mode the Arduino will enter.

2. Step 2: Differentiate from sleep execution

   The function sleep_cpu() actually puts the CPU to sleep, but does not set the mode.

3. Final Answer:

   set_sleep_mode() -> Option A

4. Quick Check:

   Set mode = set_sleep_mode() [OK]

Hint: Set mode first with set_sleep_mode() before sleeping [OK]

Common Mistakes:

• Confusing set_sleep_mode() with sleep_cpu()
• Thinking attachInterrupt() sets sleep mode
• Using delay() to enter sleep

2. Which of the following is the correct syntax to put the Arduino into sleep mode after setting it?

easy

A. sleep_mode();

B. sleep_cpu();

C. sleep();

D. enter_sleep();

Solution

1. Step 1: Identify the sleep function

   The function sleep_cpu() is the correct call to put the CPU into sleep mode after setting it.

2. Step 2: Check other options

   sleep_mode() is not a valid function, nor are sleep() or enter_sleep().

3. Final Answer:

   sleep_cpu(); -> Option B

4. Quick Check:

   Sleep call = sleep_cpu() [OK]

Hint: Use sleep_cpu() to enter sleep after setting mode [OK]

Common Mistakes:

• Using sleep_mode() instead of sleep_cpu()
• Trying to call sleep() which doesn't exist
• Confusing function names

3. What will the following Arduino code do?

set_sleep_mode(SLEEP_MODE_PWR_DOWN);
sleep_enable();
sleep_cpu();
// CPU sleeps here
sleep_disable();

medium

A. The CPU enters power-down sleep mode and stays asleep until an interrupt wakes it

B. The CPU enters power-down sleep mode and wakes immediately

C. The CPU does not sleep because sleep_enable() is missing

D. The CPU enters idle mode instead of power-down

Solution

1. Step 1: Analyze sleep mode setting

   The code sets the sleep mode to power-down with set_sleep_mode(SLEEP_MODE_PWR_DOWN);.

2. Step 2: Understand sleep flow

   Calling sleep_enable() then sleep_cpu() puts the CPU to sleep in power-down mode. It stays asleep until an interrupt or reset wakes it. After waking, sleep_disable() disables sleep.

3. Final Answer:

   The CPU enters power-down sleep mode and stays asleep until an interrupt wakes it -> Option A

4. Quick Check:

   Power-down sleep = stays asleep until interrupt [OK]

Hint: Power-down sleep waits for interrupt to wake CPU [OK]

Common Mistakes:

• Assuming CPU wakes immediately without interrupt
• Forgetting sleep_enable() disables sleep
• Confusing idle mode with power-down

4. Identify the error in this Arduino sleep code snippet:

set_sleep_mode(SLEEP_MODE_IDLE);
sleep_cpu();
sleep_enable();

medium

A. set_sleep_mode() is missing a parameter

B. No error, code is correct

C. sleep_cpu() should be replaced with sleep_mode()

D. sleep_enable() must be called before sleep_cpu()

Solution

1. Step 1: Check function order

   The function sleep_enable() must be called before sleep_cpu() to enable sleep mode properly.

2. Step 2: Verify other parts

   set_sleep_mode() is correctly called with a valid mode. sleep_cpu() is the correct function to enter sleep.

3. Final Answer:

   sleep_enable() must be called before sleep_cpu() -> Option D

4. Quick Check:

   Enable sleep before sleeping [OK]

Hint: Call sleep_enable() before sleep_cpu() to avoid errors [OK]

Common Mistakes:

• Calling sleep_cpu() before sleep_enable()
• Confusing sleep_cpu() with sleep_mode()
• Missing parameters in set_sleep_mode()

5. You want to save maximum power on your Arduino but still wake it up using a button press on pin 2. Which sleep mode and wake method should you use?

hard

A. Use SLEEP_MODE_IDLE and poll the button in loop()

B. Use SLEEP_MODE_STANDBY and wake with delay()

C. Use SLEEP_MODE_PWR_DOWN and attach an external interrupt on pin 2

D. Use SLEEP_MODE_ADC and check button state with analogRead()

Solution

1. Step 1: Choose lowest power sleep mode

   SLEEP_MODE_PWR_DOWN uses the least power by shutting down most parts of the chip.

2. Step 2: Select wake method

   To wake from power-down mode, an external interrupt on pin 2 (using attachInterrupt) is needed because polling or delay() won't wake the CPU.

3. Final Answer:

   Use SLEEP_MODE_PWR_DOWN and attach an external interrupt on pin 2 -> Option C

4. Quick Check:

   Lowest power + external interrupt wake = Use SLEEP_MODE_PWR_DOWN and attach an external interrupt on pin 2 [OK]

Hint: Lowest power sleep needs external interrupt wake [OK]

Common Mistakes:

• Using idle mode which uses more power
• Trying to wake with delay() which doesn't work
• Polling button instead of using interrupt