LowPower library usage in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after running this Arduino sketch?

Consider the following Arduino code using the LowPower library. What will be printed to the serial monitor after the device wakes up from sleep?

Arduino

#include <LowPower.h>

void setup() {
  Serial.begin(9600);
  delay(1000); // Wait for serial to initialize
  Serial.println("Start");
  LowPower.powerDown(SLEEP_2S, ADC_OFF, BOD_OFF);
  Serial.println("Wake up");
}

void loop() {
  // Empty loop
}

A Start\nWake up

B Wake up\nStart

C Start

D Wake up

💡 Hint

Think about what happens before and after the sleep function.

The code prints "Start" first, then goes to sleep for 2 seconds. After waking up, it prints "Wake up".

❓ Predict Output

intermediate

How long does the Arduino sleep in this code?

Given this code snippet using the LowPower library, how many seconds will the Arduino sleep before waking up?

Arduino

#include <LowPower.h>

void setup() {
  LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF);
  LowPower.powerDown(SLEEP_4S, ADC_OFF, BOD_OFF);
  LowPower.powerDown(SLEEP_2S, ADC_OFF, BOD_OFF);
}

void loop() {}

A 4 seconds

B 2 seconds

C 14 seconds

D 8 seconds

💡 Hint

Add the sleep durations together.

The Arduino sleeps for 8 + 4 + 2 seconds sequentially, totaling 14 seconds.

❓ Predict Output

advanced

What error occurs when calling LowPower.powerDown() without setup() initialization?

What will happen if you call LowPower.powerDown(SLEEP_1S, ADC_OFF, BOD_OFF) inside loop() without calling Serial.begin() or any setup initialization?

Arduino

void setup() {
  // Empty setup
}

void loop() {
  LowPower.powerDown(SLEEP_1S, ADC_OFF, BOD_OFF);
  Serial.println("Awake");
  delay(1000);
}

A No output, Serial.println causes no output because Serial not initialized

B Compilation error due to missing Serial.begin()

C Prints "Awake" every second

D Runtime error: LowPower library not initialized

💡 Hint

Think about what happens if Serial is used without initialization.

Serial.println() will not output anything because Serial.begin() was never called, but no compilation or runtime error occurs.

❓ Predict Output

advanced

What is the effect of BOD_ON in LowPower.powerDown()?

In the LowPower library, what happens if you use BOD_ON instead of BOD_OFF in the powerDown() function?

Arduino

LowPower.powerDown(SLEEP_4S, ADC_OFF, BOD_ON);

A Brown-out detector is disabled, saving power

B Brown-out detector triggers a reset immediately

C Brown-out detector causes a compilation error

D Brown-out detector stays on during sleep, consuming more power

💡 Hint

BOD stands for Brown-Out Detector.

BOD_ON keeps the brown-out detector active during sleep, which uses more power but protects against low voltage resets.

🧠 Conceptual

expert

Which option correctly describes the behavior of LowPower.idle() mode?

Select the statement that best describes what happens when the Arduino enters LowPower.idle() mode.

A All clocks and peripherals are stopped, device consumes minimum power

B CPU is stopped but peripherals like timers and serial continue running

C CPU and ADC are stopped but timers continue running

D Device resets immediately after entering idle mode

💡 Hint

Idle mode is the lightest sleep mode.

In idle mode, the CPU stops but peripherals like timers and serial communication keep running, allowing quick wake-up.