LowPower library usage in Arduino - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of the LowPower library in Arduino?

The LowPower library helps reduce power consumption by putting the Arduino into sleep modes during idle times, saving battery life.

beginner

How do you put an Arduino into sleep mode using the LowPower library?

You call a function like LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF); to put the Arduino into a low power sleep for 8 seconds, turning off ADC and Brown-out Detector to save power.

beginner

What does the parameter SLEEP_8S mean in the LowPower library?

It means the Arduino will sleep for 8 seconds before waking up automatically.

intermediate

Why would you turn off the ADC and BOD in sleep mode?

Turning off the ADC (Analog to Digital Converter) and BOD (Brown-out Detector) reduces power consumption further because these components use power even when the Arduino is sleeping.

intermediate

Can the Arduino wake up from sleep mode using an external interrupt with the LowPower library?

Yes, the Arduino can wake up from sleep mode when an external interrupt occurs, allowing it to respond to events while still saving power.

Which function puts the Arduino into a low power sleep mode for a set time?

A delay()

B analogRead()

C digitalWrite()

D LowPower.powerDown()

LowPower.powerDown() is used to put the Arduino into sleep mode for a specified duration.

What does turning off ADC during sleep do?

A Saves power by disabling analog to digital conversion

B Prevents the Arduino from waking up

C Makes the Arduino run faster

D Increases power consumption

Disabling ADC saves power because the analog to digital converter won't use energy while sleeping.

How can the Arduino wake up from sleep mode when using the LowPower library?

A By an external interrupt or timer

B By pressing the reset button only

C Only after the sleep timer ends

D It cannot wake up automatically

The Arduino can wake up from sleep mode by an external interrupt or when the sleep timer expires.

What does BOD_OFF do in the LowPower library sleep function?

A Disables the battery

B Turns off the Brown-out Detector to save power

C Turns off the board

D Enables the Brown-out Detector

BOD_OFF disables the Brown-out Detector during sleep to reduce power consumption.

Which of these is NOT a sleep duration option in the LowPower library?

A SLEEP_4S

B SLEEP_1S

C SLEEP_16S

D SLEEP_8S

SLEEP_16S is not a standard sleep duration option; common options include 1s, 2s, 4s, 8s.

Explain how to use the LowPower library to put an Arduino into sleep mode and wake it up with an external event.

Think about how to save power and still respond to buttons or sensors.

Describe why turning off ADC and BOD during sleep helps save power on an Arduino.

Consider what parts of the Arduino keep working even when sleeping.

Practice

1.

What is the main purpose of the LowPower library in Arduino?

easy

A. To connect Arduino to the internet

B. To increase the speed of the Arduino processor

C. To add more memory to the Arduino

D. To put the Arduino into sleep mode to save battery power

Solution

1. Step 1: Understand the LowPower library function

   The LowPower library is designed to reduce power consumption by putting the Arduino into sleep mode.

2. Step 2: Compare options with the library purpose

   Options B, C, and D do not relate to power saving or sleep mode, only To put the Arduino into sleep mode to save battery power matches the purpose.

3. Final Answer:

   To put the Arduino into sleep mode to save battery power -> Option D

4. Quick Check:

   LowPower library = Sleep mode for saving power [OK]

Hint: LowPower library = sleep mode to save battery [OK]

Common Mistakes:

• Thinking it speeds up the processor
• Confusing it with memory or internet functions
• Assuming it runs code faster

2.

Which of the following is the correct syntax to put Arduino to sleep for 8 seconds using the LowPower library?

LowPower._____();

easy

A. powerDown(SLEEP_8S, ADC_OFF, BOD_OFF)

B. sleep(8)

C. sleepMode(8)

D. sleepFor(8s)

Solution

1. Step 1: Recall LowPower sleep syntax

   The LowPower library uses powerDown() with parameters for sleep duration and power settings.

2. Step 2: Match correct parameters for 8 seconds sleep

   SLEEP_8S is the constant for 8 seconds, and ADC and BOD are turned off for power saving.

3. Final Answer:

   powerDown(SLEEP_8S, ADC_OFF, BOD_OFF) -> Option A

4. Quick Check:

   LowPower powerDown with SLEEP_8S = correct syntax [OK]

Hint: Use powerDown with SLEEP_8S for 8 seconds sleep [OK]

Common Mistakes:

• Using sleep(8) which is not a LowPower function
• Adding units like '8s' in function calls
• Using incorrect function names like sleepMode

3.

What will be the output on the serial monitor after running this code snippet?

#include <LowPower.h>

void setup() {
  Serial.begin(9600);
  Serial.println("Start");
  LowPower.powerDown(SLEEP_4S, ADC_OFF, BOD_OFF);
  Serial.println("Wake up");
}

void loop() {}

medium

A. Start\nWake up

B. Start

C. Wake up

D. No output

Solution

1. Step 1: Analyze setup() execution

   The code prints "Start", then sleeps for 4 seconds, then prints "Wake up".

2. Step 2: Understand sleep effect on Serial output

   Sleeping pauses the CPU but does not stop the program flow; after sleep, it continues to print "Wake up".

3. Final Answer:

   Start\nWake up -> Option A

4. Quick Check:

   Sleep pauses, then continues printing [OK]

Hint: Sleep pauses but code continues after wake [OK]

Common Mistakes:

• Thinking sleep stops all code permanently
• Expecting no output after sleep
• Confusing sleep with reset

4.

Identify the error in this code using the LowPower library:

#include <LowPower.h>

void setup() {
  LowPower.powerDown(SLEEP_1S, ADC_OFF);
}

void loop() {}

medium

A. powerDown should be called in loop(), not setup()

B. Incorrect library include syntax

C. Missing third parameter for powerDown function

D. SLEEP_1S is not a valid sleep duration

Solution

1. Step 1: Check powerDown function parameters

   The powerDown function requires three parameters: sleep duration, ADC state, and BOD state.

2. Step 2: Identify missing parameter

   The code only provides two parameters, missing the BOD_OFF or BOD_ON parameter.

3. Final Answer:

   Missing third parameter for powerDown function -> Option C

4. Quick Check:

   powerDown needs 3 params: duration, ADC, BOD [OK]

Hint: powerDown always needs 3 parameters [OK]

Common Mistakes:

• Omitting the BOD parameter
• Calling powerDown in setup is allowed
• Assuming SLEEP_1S is invalid

5.

You want your Arduino to sleep for 8 seconds repeatedly until a button press wakes it up. Which code snippet correctly uses the LowPower library to achieve this?

void loop() {
  // Sleep for 8 seconds
  LowPower.powerDown(_____, ADC_OFF, BOD_OFF);
  // Check button press here
}

hard

A. SLEEP_FOREVER

B. SLEEP_8S

C. SLEEP_16S

D. SLEEP_4S

Solution

1. Step 1: Identify sleep duration constant for 8 seconds

   The LowPower library defines SLEEP_8S for 8 seconds sleep intervals.

2. Step 2: Confirm repeated sleep in loop

   Calling powerDown with SLEEP_8S inside loop will sleep repeatedly for 8 seconds until interrupted.

3. Final Answer:

   SLEEP_8S -> Option B

4. Quick Check:

   Use SLEEP_8S for 8 seconds sleep [OK]

Hint: Use SLEEP_8S for 8 seconds sleep in loop [OK]

Common Mistakes:

• Using SLEEP_FOREVER which is not a valid duration
• Choosing invalid SLEEP_16S
• Choosing shorter sleep times like SLEEP_4S