Aaron Ardiri
[Valid RSS] RSS/XML feed
198 entries available (show all)


Internet of Things (IoT)

RIoT Secure AB


This type of dog wont be chasing the mail man or other intruders any time soon.

Do you have an Arduino project configured to periodically gather some sensory information and you are noticing it draining power quickly while waiting for the next interval? Do you want to get the maximum operating period on those small batteries? Then it is time to consider implementing a WatchDog Timer (WDT) so conserve power when it is not in use.

So, what is a watchdog timer?

  • A watchdog timer (WDT); sometimes called a computer operating properly or COP timer, or simply a watchdog - is an electronic timer that is used to detect and recover from computer malfunctions.
    source: en.wikipedia.org/wiki/Watchdog_timer

While typically used to detect when a computer system crashes or becomes unresponsive - it can also be used to wake up a device if it has been on purpose put into a power down state; something that becomes applicable to saving power and reducing power consumption.

You could theoretically write your own; using the in-built features of the Atmel AVR platform - specifically the <avr/wdt.h>, <avr/sleep.h>, <avr/power.h> and <avr/interrupt.h> headers or you could use a third-party library and save yourself a few headaches.


Low-Power Project Home, Blog CC-SA 3.0
JeeLib Project Home, Wiki MIT
narcoleptic Project Home GNU GPL v3.0
Enerlib Project Home undefined

I found the above four libraries; some in better states than others and depending on the type of open-source license you are looking for the one you decide on will vary. I took a look at the code state of each project and I believe the "Low-Power" library is streamlined well and very simple to integrate into an existing Arduino project.

The Low-Power library provides three example cases; either to put the device in idle mode for a short timeframe or do a full power down and wake-up after a period of time or after an external interrupt occurs (ie: Serial, sensor or a network event).

  • #include "LowPower.h"
    void setup()
      // No setup is required for this library
    void loop() 
      // Enter power down state for 8 s with ADC and BOD module disabled
      LowPower.powerDown(SLEEP_8S, ADC_OFF, BOD_OFF);  
      // Do something here
      // Example: Read sensor, data logging, data transmission.

The above code puts to device to sleep for eight seconds (the maximum interval provided by the AVR hardware) - you could make multiple requests to extend this (2x8 = 16 seconds) or if you want you could hook up an external timer and trigger the wake-up with an interrupt. It also increases the basic compiled sketch size from 450 to 642 bytes (using 1.5.x IDE) and adds a single byte of dynamic memory for the LowPower reference object - minimal for the job.

But while it sounds great - there is a small caveat; power reduction relies not only on software but it also relies on the hardware used (off the shelf devices are not very power efficient).

I found a great blog post comparing the power consumption of an Arduino UNO by default with a watchdog timer (45.6mA vs 34.4mA - a small reduction) and using a custom board removing any power hungry components such as regulators and LEDs; to get right down to µA levels. Rocket Scream have a blog post outlining similar results.

This blog post was also posted on the Evothings blog


advertisement (self plug):
need assistance in an IoT project? contact us for a free consultation.


B4RM4N - Make the perfect cocktail every time
TinyScreen - A perfect compliment to the TinyDuino

All content provided on this blog is for informational purposes only.
All comments are generated by users and moderated for inappropriateness periodically.
The owner will not be liable for any losses, injuries, or damages from the display or use of this information.