Timer interrupts with TimerOne library in Arduino - Mini Project: Build & Apply

Timer interrupts with TimerOne library

📖 Scenario: You want to blink an LED on your Arduino board at a steady pace without using the delay() function. Using timer interrupts helps you do this efficiently.

🎯 Goal: Build a program that uses the TimerOne library to blink the built-in LED every 1 second using timer interrupts.

📋 What You'll Learn

Use the TimerOne library to set up a timer interrupt

Create an interrupt service routine (ISR) to toggle the LED

Set the timer to trigger every 1 second (1000000 microseconds)

Use the built-in LED on pin 13

💡 Why This Matters

🌍 Real World

Timer interrupts are used in real devices to perform tasks regularly without stopping other work, like blinking status lights or reading sensors.

💼 Career

Understanding timer interrupts is important for embedded systems programming, robotics, and hardware control jobs.

1

Set up the LED pin

Create a variable called ledPin and set it to 13. Then, in the setup() function, set ledPin as an output using pinMode(ledPin, OUTPUT);.

Arduino

int ledPin = 13;

void setup() {
  pinMode(ledPin, OUTPUT);
  // Your code here
}

void loop() {
  // Empty loop
}

Hint

Use int ledPin = 13; and pinMode(ledPin, OUTPUT); inside setup().

2

Include TimerOne library and declare a volatile variable

Add #include <TimerOne.h> at the top. Then, create a volatile bool ledState variable and set it to false to track the LED state.

Arduino

#include 

int ledPin = 13;
volatile bool ledState = false;

void setup() {
  pinMode(ledPin, OUTPUT);
  // Your code here
}

void loop() {
  // Empty loop
}

Hint

Include the TimerOne library and declare volatile bool ledState = false; before setup().

3

Set up TimerOne to call the interrupt function every 1 second

In the setup() function, add Timer1.initialize(1000000); to set the timer for 1 second intervals. Then add Timer1.attachInterrupt(toggleLED); to call the toggleLED function on each interrupt. Also, write the toggleLED() function that toggles ledState and sets the LED pin accordingly.

Arduino

#include 

int ledPin = 13;
volatile bool ledState = false;

void setup() {
  pinMode(ledPin, OUTPUT);
  Timer1.initialize(1000000); // 1 second
  Timer1.attachInterrupt(toggleLED);
  // Your code here
}

void loop() {
  // Empty loop
}

void toggleLED() {
  ledState = !ledState;
  digitalWrite(ledPin, ledState);
}

Hint

Use Timer1.initialize(1000000); and Timer1.attachInterrupt(toggleLED); in setup(). Define toggleLED() to flip ledState and write it to ledPin.

4

Print a message to confirm the program is running

In the setup() function, add Serial.begin(9600); to start serial communication. Then add Serial.println("Timer interrupt started"); to print a confirmation message.

Arduino

#include 

int ledPin = 13;
volatile bool ledState = false;

void setup() {
  pinMode(ledPin, OUTPUT);
  Timer1.initialize(1000000); // 1 second
  Timer1.attachInterrupt(toggleLED);
  Serial.begin(9600);
  // Your code here
}

void loop() {
  // Empty loop
}

void toggleLED() {
  ledState = !ledState;
  digitalWrite(ledPin, ledState);
}

Hint

Use Serial.begin(9600); and Serial.println("Timer interrupt started"); in setup().

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