Timer interrupts with TimerOne library in Arduino - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the TimerOne library in Arduino?

The TimerOne library allows you to easily set up and use Timer1 on Arduino boards to create timer interrupts for precise timing tasks.

beginner

How do you initialize TimerOne to trigger an interrupt every 1 second?

You use Timer1.initialize(1000000); where 1000000 is the time in microseconds (1 second).

beginner

What function do you use to attach an interrupt service routine (ISR) with TimerOne?

You use Timer1.attachInterrupt(yourISR); where yourISR is the function called when the timer interrupt occurs.

intermediate

Why should the code inside an ISR be kept short and fast?

Because the ISR blocks other code and interrupts, keeping it short prevents delays and keeps the program responsive.

beginner

How do you stop TimerOne interrupts once they are running?

You call Timer1.detachInterrupt(); to stop the timer interrupt from firing.

Which Timer does the TimerOne library control on Arduino boards?

A Timer0

B Timer2

C Timer1

D Timer3

TimerOne library specifically controls Timer1 on Arduino boards.

What unit of time does Timer1.initialize() expect as its argument?

A Microseconds

B Nanoseconds

C Seconds

D Milliseconds

Timer1.initialize() expects the time interval in microseconds.

What is the correct way to attach an interrupt function named blinkLED using TimerOne?

A Timer1.setInterrupt(blinkLED);

B Timer1.attachInterrupt(blinkLED);

C attachInterrupt(Timer1, blinkLED);

D Timer1.interrupt(blinkLED);

The correct method is Timer1.attachInterrupt(yourFunction);

What happens if an ISR takes too long to execute?

A The Arduino resets automatically

B The program runs faster

C The ISR is skipped

D Other interrupts and code are delayed

Long ISRs block other code and interrupts, causing delays.

How do you stop TimerOne interrupts once started?

A Timer1.detachInterrupt();

B Timer1.disable();

C Timer1.stop();

D Timer1.end();

Timer1.detachInterrupt() stops the timer interrupt.

Explain how to set up a timer interrupt using the TimerOne library to toggle an LED every half second.

Think about initialize(), attachInterrupt(), and what code runs inside the ISR.

Describe why timer interrupts are useful in Arduino projects and how TimerOne simplifies their use.

Consider how interrupts help multitasking and timing.

Practice

1. What is the main purpose of using the TimerOne library in Arduino programming?

easy

A. To run code at precise time intervals using interrupts

B. To control the speed of the Arduino board

C. To manage power consumption automatically

D. To connect Arduino to the internet

Solution

1. Step 1: Understand TimerOne library role

   The TimerOne library is designed to help run code at exact time intervals by using hardware timer interrupts.

2. Step 2: Compare options with library purpose

   Only To run code at precise time intervals using interrupts correctly describes this purpose. Other options describe unrelated features.

3. Final Answer:

   To run code at precise time intervals using interrupts -> Option A

4. Quick Check:

   TimerOne = precise timed interrupts [OK]

Hint: TimerOne = precise timing with interrupts [OK]

Common Mistakes:

• Thinking TimerOne controls Arduino speed
• Confusing interrupts with internet connection
• Assuming it manages power automatically

2. Which of the following is the correct way to start TimerOne with a 1-second interval?

easy

A. Timer1.initialize(1000000);

B. Timer1.start(1000);

C. Timer1.setInterval(1);

D. Timer1.begin(1000);

Solution

1. Step 1: Recall TimerOne initialization syntax

   The TimerOne library uses initialize() with microseconds as argument to set the timer interval.

2. Step 2: Match 1 second to microseconds

   1 second = 1,000,000 microseconds, so initialize(1000000) is correct.

3. Final Answer:

   Timer1.initialize(1000000); -> Option A

4. Quick Check:

   initialize uses microseconds = 1000000 [OK]

Hint: Use initialize() with microseconds for timing [OK]

Common Mistakes:

• Using milliseconds instead of microseconds
• Using non-existent start() or begin() methods
• Confusing setInterval() with initialize()

3. What will be the output on the Serial Monitor if this code runs?

void blink() {
  Serial.println("Tick");
}

void setup() {
  Serial.begin(9600);
  Timer1.initialize(500000);
  Timer1.attachInterrupt(blink);
}

void loop() {
  // empty
}

medium

A. No output because loop is empty

B. Prints "Tick" once and stops

C. Prints "Tick" every 0.5 seconds repeatedly

D. Prints "Tick" continuously without delay

Solution

1. Step 1: Understand Timer1 setup

   Timer1 is initialized to 500000 microseconds (0.5 seconds) and blink() is attached as interrupt.

2. Step 2: Analyze interrupt behavior

   Every 0.5 seconds, blink() runs and prints "Tick" to Serial Monitor repeatedly.

3. Final Answer:

   Prints "Tick" every 0.5 seconds repeatedly -> Option C

4. Quick Check:

   attachInterrupt triggers blink() repeatedly [OK]

Hint: attachInterrupt runs function repeatedly at interval [OK]

Common Mistakes:

• Thinking loop() must print for output
• Assuming interrupt runs only once
• Confusing timing units causing wrong intervals

4. Identify the error in this TimerOne usage:

void blink() {
  digitalWrite(13, !digitalRead(13));
}

void setup() {
  pinMode(13, OUTPUT);
  Timer1.initialize(1000000);
  Timer1.attachInterrupt(blink());
}

void loop() {}

medium

A. Timer1.initialize() argument should be in milliseconds

B. Missing Serial.begin() in setup()

C. Pin 13 cannot be used with TimerOne interrupts

D. Incorrect call: attachInterrupt(blink()) should be attachInterrupt(blink)

Solution

1. Step 1: Check attachInterrupt usage

   attachInterrupt expects a function pointer, so it should be attachInterrupt(blink), not attachInterrupt(blink()).

2. Step 2: Verify other parts

   Serial.begin() is not needed here, pin 13 can be toggled, and initialize() uses microseconds correctly.

3. Final Answer:

   Incorrect call: attachInterrupt(blink()) should be attachInterrupt(blink) -> Option D

4. Quick Check:

   attachInterrupt needs function name, no parentheses [OK]

Hint: Pass function name without () to attachInterrupt [OK]

Common Mistakes:

• Calling function with () inside attachInterrupt
• Confusing microseconds with milliseconds
• Thinking Serial.begin() is always required

5. You want to toggle an LED every 200ms using TimerOne. Which code snippet correctly sets this up?

hard

A. Timer1.initialize(200);
Timer1.attachInterrupt(blink);

B. Timer1.initialize(200000);
Timer1.attachInterrupt([](){ digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN)); });

C. Timer1.start(200000);
Timer1.attachInterrupt(blink());

D. Timer1.setInterval(200000);
Timer1.attachInterrupt(blink);

Solution

1. Step 1: Convert 200ms to microseconds

   200 milliseconds = 200,000 microseconds, so initialize(200000) is correct.

2. Step 2: Check attachInterrupt syntax and function

   Using a lambda function without parentheses is valid and toggles LED correctly. Other options use wrong methods or call functions incorrectly.

3. Final Answer:

   Timer1.initialize(200000); Timer1.attachInterrupt([](){ digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN)); }); -> Option B

4. Quick Check:

   initialize with microseconds + correct attachInterrupt [OK]

Hint: Use initialize(microseconds) and attachInterrupt with function [OK]

Common Mistakes:

• Using milliseconds instead of microseconds
• Calling function with () inside attachInterrupt
• Using non-existent start() or setInterval() methods