Reducing power consumption tips in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Arduino sleep mode code?

Consider this Arduino sketch that puts the microcontroller into a low power sleep mode. What will be printed on the serial monitor?

Arduino

void setup() {
  Serial.begin(9600);
  delay(1000);
  Serial.println("Going to sleep...");
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  sleep_enable();
  sleep_cpu();
  Serial.println("Awake!");
}

void loop() {
  // Empty loop
}

A Going to sleep...\nAwake!

B Going to sleep...

C Awake!

D No output, program hangs

💡 Hint

Is there any wake-up source (like an interrupt) configured to exit power-down sleep mode?

The code prints "Going to sleep...", then enters power-down sleep mode. Without a wake-up source, the MCU never wakes up and "Awake!" is never printed.

🧠 Conceptual

intermediate

Which method reduces power consumption the most in Arduino?

Among these options, which is the most effective way to reduce power consumption in an Arduino project?

A Use delay() to pause the program

B Keep all peripherals running at all times

C Increase the clock speed

D Put the MCU into deep sleep mode when idle

💡 Hint

Think about what consumes power when the MCU is idle.

Deep sleep mode turns off most parts of the MCU, saving the most power.

🔧 Debug

advanced

Why does this Arduino code not reduce power consumption as expected?

This code tries to reduce power by turning off the ADC, but power consumption remains high. What is the problem?

Arduino

void setup() {
  ADCSRA &= ~(1 << ADEN); // Disable ADC
}

void loop() {
  // Do nothing
}

A ADC is disabled correctly; problem is elsewhere

B ADCSRA register is write-protected and cannot be changed

C ADEN bit must be cleared with ADCSRA = ADCSRA & ~(1 << ADEN); not &= operator

D ADC must be disabled after sleep mode is set

💡 Hint

Check if disabling ADC alone is enough to reduce power.

Disabling ADC is done correctly, but other peripherals or settings may keep power high.

📝 Syntax

advanced

Which option correctly disables the Brown-out Detector (BOD) during sleep to save power?

Select the correct Arduino code snippet that disables the BOD during sleep to reduce power consumption.

A sleep_disable_bod(); sleep_cpu();

B disable_bod_sleep(); sleep_cpu();

C sleep_bod_disable(); sleep_cpu();

D bod_sleep_disable(); sleep_cpu();

💡 Hint

Look for the exact function name in the Arduino sleep library.

The function sleep_bod_disable() disables BOD during sleep correctly.

🚀 Application

expert

How many times will the wake-up function be called after this power-saving timer setup?

This Arduino code sets up a timer to wake the MCU every second for 5 seconds. How many times will the wake-up function be called?

Arduino

volatile int wakeCount = 0;

ISR(TIMER1_COMPA_vect) {
  wakeCount++;
}

void setup() {
  noInterrupts();
  TCCR1A = 0;
  TCCR1B = 0;
  TCNT1 = 0;
  OCR1A = 15624; // 1 second at 16MHz with prescaler 1024
  TCCR1B |= (1 << WGM12);
  TCCR1B |= (1 << CS12) | (1 << CS10);
  TIMSK1 |= (1 << OCIE1A);
  interrupts();
}

void loop() {
  if (wakeCount >= 5) {
    // Stop timer
    TIMSK1 &= ~(1 << OCIE1A);
    while(1); // Stop here
  }
}

A 5

B 4

C 6

D 0

💡 Hint

Count how many times the interrupt increments wakeCount before stopping.

The interrupt triggers every second and increments wakeCount until it reaches 5, then stops.