micros() for microsecond precision in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the current time in microseconds.

Arduino

unsigned long currentTime = [1]();

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

Amillis

Bmicros

Cdelay

DdigitalRead

Attempts:

3 left

💡 Hint

Common Mistakes

Using millis() instead of micros() which gives milliseconds, not microseconds.

Using delay() which pauses the program instead of returning time.

The micros() function returns the number of microseconds since the Arduino board began running the current program.

2fill in blank

medium

Complete the code to calculate elapsed time in microseconds.

Arduino

unsigned long startTime = micros();
// some code here
unsigned long elapsed = [1]() - startTime;

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

Amillis

BdigitalRead

Cdelay

Dmicros

Attempts:

3 left

💡 Hint

Common Mistakes

Using millis() to subtract from micros() which mixes units.

Using delay() which does not return time.

To measure elapsed time in microseconds, use micros() again and subtract the start time.

3fill in blank

hard

Fix the error in the code to correctly measure a 100 microsecond delay.

Arduino

unsigned long start = micros();
while (micros() - start < [1]) {
  // wait
}

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

A1000

B10

C100

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1000 which is 1 millisecond, not 100 microseconds.

Using 10 or 1 which are too short delays.

The code waits until 100 microseconds have passed. The blank should be 100 to match the desired delay.

4fill in blank

hard

Fill both blanks to create a dictionary of words and their lengths, filtering words longer than 3 characters.

Arduino

std::map<std::string, int> wordLengths;
for (const auto& word : words) {
  if (word.length() [1] 3) {
    wordLengths[word] = [2];
  }
}

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

A>

Bword.length()

C<

Dword.size()

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the condition.

Assigning the length with a wrong method.

The condition checks if the word length is greater than 3. The length is assigned using word.size().

5fill in blank

hard

Fill all three blanks to create a map of uppercase words to their lengths, filtering words longer than 4 characters.

Arduino

std::map<std::string, int> wordMap;
for (const auto& word : words) {
  if (word.length() [1] 4) {
    std::string upperWord = [2];
    wordMap[[3]] = word.length();
  }
}

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

A<

Bword

DtoUpperCase(word)

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '<' in the condition.

Not converting the word to uppercase before using as key.

The condition uses '<' to filter words shorter than 4 characters. The uppercase word is created by toUpperCase(word) and used as the key.

Practice

1. What does the Arduino function micros() return?

easy

A. The number of microseconds since the program started

B. The number of milliseconds since the program started

C. The current time in seconds

D. The number of seconds since the last reset

Solution

1. Step 1: Understand the purpose of micros()

   The micros() function returns the time in microseconds since the Arduino program began running.

2. Step 2: Compare options with the function's behavior

   Only The number of microseconds since the program started correctly states it returns microseconds since start. Others mention milliseconds or seconds, which are incorrect.

3. Final Answer:

   The number of microseconds since the program started -> Option A

4. Quick Check:

   micros() = microseconds since start [OK]

Hint: Remember micros() counts microseconds from program start [OK]

Common Mistakes:

• Confusing micros() with millis()
• Thinking it returns seconds
• Assuming it resets every second

2. Which of the following is the correct way to store the current microsecond count in a variable?

easy

A. unsigned long time = micros();

B. int time = micros();

C. float time = micros();

D. long time = micros();

Solution

1. Step 1: Identify the data type returned by micros()

   The micros() function returns an unsigned long integer representing microseconds.

2. Step 2: Match the correct variable type to store the value

   Only unsigned long can hold the large values from micros() without overflow or sign issues.

3. Final Answer:

   unsigned long time = micros(); -> Option A

4. Quick Check:

   Use unsigned long for micros() values [OK]

Hint: Use unsigned long to store micros() values safely [OK]

Common Mistakes:

• Using int which is too small
• Using float which loses precision
• Using signed long which can cause negative values

3. What will be the output of this Arduino code snippet?

unsigned long start = micros();
// some delay here
unsigned long end = micros();
unsigned long diff = end - start;
Serial.println(diff);

Assuming the delay is about 500 microseconds.

medium

A. Always zero

B. A number close to 500000

C. A negative number

D. A number close to 500

Solution

1. Step 1: Understand the timing measurement

   The code measures the time difference in microseconds between two calls to micros().

2. Step 2: Interpret the delay and difference calculation

   If the delay is about 500 microseconds, the difference diff will be close to 500, printed as a positive number.

3. Final Answer:

   A number close to 500 -> Option D

4. Quick Check:

   diff = end - start ≈ 500 [OK]

Hint: Subtract micros() values to get elapsed microseconds [OK]

Common Mistakes:

• Expecting milliseconds instead of microseconds
• Thinking difference can be negative
• Confusing delay units

4. Identify the error in this Arduino code snippet:

unsigned long start = micros();
// some code
unsigned long end = micros();
int elapsed = end - start;
Serial.println(elapsed);

medium

A. micros() cannot be assigned to unsigned long

B. Using int for elapsed can cause overflow

C. Serial.println cannot print integers

D. Subtracting micros() values is invalid

Solution

1. Step 1: Check variable types for time difference

   The difference between two micros() values can be very large, exceeding the range of int.

2. Step 2: Understand overflow risk

   Using int (usually 16-bit) can cause overflow and incorrect negative values. It should be unsigned long.

3. Final Answer:

   Using int for elapsed can cause overflow -> Option B

4. Quick Check:

   Use unsigned long for elapsed time to avoid overflow [OK]

Hint: Use unsigned long, not int, for time differences [OK]

Common Mistakes:

• Using int instead of unsigned long
• Thinking micros() returns signed values
• Assuming Serial.println can't print integers

5. You want to measure how long a button is pressed in microseconds using micros(). Which approach correctly handles the timing even if the program runs longer than 70 minutes (when micros() overflows)?

hard

A. Ignore overflow because it never affects timing

B. Reset the Arduino every 60 minutes to avoid overflow

C. Store start time, then calculate elapsed as micros() - start using unsigned long subtraction

D. Use millis() instead because it never overflows

Solution

1. Step 1: Understand micros() overflow behavior

   micros() overflows roughly every 70 minutes, wrapping back to zero.

2. Step 2: Use unsigned long subtraction to handle overflow

   Unsigned subtraction correctly calculates elapsed time even if overflow happens, so micros() - start works safely.

3. Final Answer:

   Store start time, then calculate elapsed as micros() - start using unsigned long subtraction -> Option C

4. Quick Check:

   Unsigned subtraction handles micros() overflow correctly [OK]

Hint: Use unsigned subtraction to handle micros() overflow safely [OK]

Common Mistakes:

• Thinking micros() never overflows
• Using millis() which has lower precision
• Resetting Arduino unnecessarily