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Hedy

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How do you implement fail-safes and watchdog timers in Arduino projects?

#failsafes #watchdogtimers #arduino #arduinouno

Implementing fail-safes and watchdog timers(What is a Watchdog?) in Arduino projects is crucial for reliability, especially in robotics, automation, and remote systems. Here's a clear guide on how to do both:

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1. What Are Fail-safes and Watchdog Timers?

  • Fail-safe: A mechanism that puts the system into a safe state when things go wrong (e.g., stopping a motor if sensor input is lost).
  • Watchdog Timer (WDT): A timer that resets the microcontroller if the software hangs or crashes.

2. Using a Watchdog Timer (WDT)
On AVR-based Arduinos (Uno, Nano, Mega)
Step-by-Step:
1. Include the Watchdog library:

cpp #include <avr/wdt.h>
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2. Enable the watchdog in setup():

cpp void setup() { wdt_enable(WDTO_2S); // Reset if no signal in 2 seconds }
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3. Reset it regularly in loop():

cpp void loop() { wdt_reset(); // Reset the timer // Your normal code here }
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If wdt_reset() is not called in time, the Arduino will reboot.

Available Timeout Options:

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Tip: Avoid long delays without wdt_reset(), or you’ll trigger an unwanted reset.

3. Implementing Fail-safes
Fail-safes depend on your application, but here are common techniques:

Example 1: Sensor Timeout

cpp unsigned long lastSensorRead = 0; const unsigned long timeout = 3000; // 3 seconds void loop() { if (readSensor()) { lastSensorRead = millis(); } if (millis() - lastSensorRead > timeout) { enterFailSafe(); // e.g., stop motors or blink LED } wdt_reset(); // Keep watchdog alive }
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Example 2: Communication Loss (e.g., Serial, RF)

cpp unsigned long lastPacket = millis(); void loop() { if (Serial.available()) { lastPacket = millis(); processData(); } if (millis() - lastPacket > 5000) { // Communication lost digitalWrite(LED_BUILTIN, HIGH); // Signal failure } wdt_reset(); }
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4. Testing the Watchdog
To simulate a lock-up:

cpp void loop() { while (true) { // Infinite loop, watchdog will reset the Arduino } }
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You’ll see the board reboot every few seconds (watchdog kicks in).

Best Practices

  • Always combine watchdog with fail-safe logic, not as a replacement.
  • Avoid delay() in watchdog code unless necessary.
  • For advanced needs (external WDT, ESP32), use dedicated libraries or hardware.

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