Timer interrupts with TimerOne library in Arduino

Introduction

Timer interrupts let your Arduino do tasks automatically at set times without stopping other work.

You want to blink an LED exactly every second without delay.

You need to measure time intervals precisely while running other code.

You want to run a function repeatedly at fixed time intervals.

You want to avoid using delay() so your program stays responsive.

Syntax

Arduino

Timer1.initialize(period_in_microseconds);
Timer1.attachInterrupt(yourFunction);

initialize() sets how often the interrupt happens in microseconds.

attachInterrupt() links your function to run each time the timer fires.

Examples

This sets the timer to call blinkLED() every 1 second.

Arduino

Timer1.initialize(1000000); // 1 second
Timer1.attachInterrupt(blinkLED);

This calls updateSensor() every half second.

Arduino

Timer1.initialize(500000); // 0.5 seconds
Timer1.attachInterrupt(updateSensor);

Sample Program

This program uses TimerOne to toggle the built-in LED every second without blocking the main loop.

Arduino

#include <TimerOne.h>

const int ledPin = 13;
volatile bool ledState = false;

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

void loop() {
  // Main code can run here without delay
}

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

Important Notes

Functions called by interrupts should be short and fast to avoid problems.

Use volatile for variables shared between interrupt and main code.

TimerOne library works on Arduino boards with 16-bit timers like Uno and Mega.

Summary

TimerOne library helps run code at exact time intervals using interrupts.

Use initialize() to set the timer period and attachInterrupt() to set the function.

Interrupt functions should be quick and use volatile for shared variables.

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