Arduino sleep modes - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of using sleep modes in Arduino?

Sleep modes help reduce power consumption by putting the Arduino into a low-power state when it is idle.

beginner

Name the common sleep modes available on Arduino.

The common sleep modes are: Idle, ADC Noise Reduction, Power-down, Power-save, Standby, and Extended Standby.

intermediate

How does the 'Power-down' sleep mode affect the Arduino?

In Power-down mode, almost all of the Arduino's functions are stopped to save maximum power, but it can still wake up from external interrupts.

beginner

Which Arduino library is commonly used to manage sleep modes?

The library is used to control sleep modes on Arduino boards based on AVR microcontrollers.

intermediate

What is the difference between 'Idle' and 'Standby' sleep modes?

Idle mode stops the CPU but keeps peripherals running, allowing quick wake-up. Standby mode stops the CPU and all clocks except the oscillator, saving more power but with a slightly longer wake-up time.

Which Arduino sleep mode saves the most power?

A Power-down

B Idle

C ADC Noise Reduction

D Standby

Power-down mode stops almost all functions, saving the most power.

Which library do you include to use sleep functions on an AVR-based Arduino?

A <LowPower.h>

B <ArduinoSleep.h>

C <avr/sleep.h>

D <SleepMode.h>

The library provides sleep mode functions for AVR Arduinos.

In which sleep mode does the CPU stop but peripherals keep running?

A Idle

B Extended Standby

C Power-down

D Power-save

Idle mode stops the CPU but keeps peripherals active.

What can wake the Arduino from Power-down mode?

A Timer interrupts only

B Both timer and external interrupts

C No interrupts can wake it

D External interrupts only

Only external interrupts can wake the Arduino from Power-down mode.

Why use sleep modes in Arduino projects?

A To increase processing speed

B To reduce power consumption

C To add more memory

D To improve sensor accuracy

Sleep modes reduce power use when the Arduino is idle.

Explain how Arduino sleep modes help save power and name at least three different modes.

Think about what happens to the CPU and peripherals in each mode.

Describe how to put an Arduino into sleep mode using the avr/sleep.h library.

Consider the steps to prepare and enter 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