AutocadHow-ToBeginner · 4 min read

How to Use Watchdog Timer in Arduino for Reliable Code

Use the avr/wdt.h library to enable the watchdog timer in Arduino. Call wdt_enable(timeout) to start it and wdt_reset() regularly in your code to prevent reset. If the timer is not reset in time, the Arduino will automatically restart.

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Syntax

The watchdog timer is controlled using functions from the avr/wdt.h library. The main functions are:

wdt_enable(timeout): Starts the watchdog timer with a specified timeout.
wdt_reset(): Resets the watchdog timer to prevent it from triggering a reset.
wdt_disable(): Turns off the watchdog timer.

The timeout parameter sets how long the watchdog waits before resetting the Arduino if wdt_reset() is not called.

arduino

#include <avr/wdt.h>

void setup() {
  // Enable watchdog timer with 2 second timeout
  wdt_enable(WDTO_2S);
}

void loop() {
  // Reset watchdog timer regularly
  wdt_reset();
  // Your code here
}

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Example

This example shows how to use the watchdog timer to reset the Arduino if the loop stops calling wdt_reset(). It blinks the built-in LED and resets the watchdog each loop. If you comment out wdt_reset(), the Arduino will reset after 2 seconds.

arduino

#include <avr/wdt.h>

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
  wdt_enable(WDTO_2S); // Enable watchdog with 2 seconds timeout
}

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);
  delay(500);
  digitalWrite(LED_BUILTIN, LOW);
  delay(500);

  wdt_reset(); // Reset watchdog timer to prevent reset
}

Output

The built-in LED blinks on and off every 0.5 seconds continuously. If wdt_reset() is removed, the Arduino resets every 2 seconds.

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Common Pitfalls

Common mistakes when using the watchdog timer include:

Not calling wdt_reset() regularly, causing unwanted resets.
Forgetting to include #include <avr/wdt.h>.
Not disabling the watchdog before uploading new code, which can cause upload failures.
Using very short timeouts that reset the board too quickly.

Always test your code with the watchdog enabled to ensure it behaves as expected.

arduino

#include <avr/wdt.h>

void setup() {
  // Wrong: Not enabling watchdog
}

void loop() {
  // Wrong: Not resetting watchdog
  delay(1000);
}

// Correct way:
// wdt_enable(WDTO_2S);
// wdt_reset(); inside loop()

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Quick Reference

Function	Description
wdt_enable(timeout)	Starts watchdog timer with timeout (e.g., WDTO_2S for 2 seconds)
wdt_reset()	Resets watchdog timer to prevent reset
wdt_disable()	Disables the watchdog timer
Timeout options	WDTO_15MS, WDTO_30MS, WDTO_60MS, WDTO_120MS, WDTO_250MS, WDTO_500MS, WDTO_1S, WDTO_2S, WDTO_4S, WDTO_8S

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Key Takeaways

Include avr/wdt.h to use the watchdog timer in Arduino.

Call wdt_enable(timeout) to start the watchdog with a timeout.

Regularly call wdt_reset() in your loop to avoid unwanted resets.

Disable the watchdog before uploading new code if needed.

Test your code carefully to ensure the watchdog behaves as expected.