Powering down for the embedded IoT
Because they build applications that must operate in resource-constrained environments, embedded developers have always had to balance energy efficiency and power consumption against the performance that their designs required.
But over the last decade not only mobile phones but wide swaths of embedded design have gone tether-less, without the security of a traditional wired power supply. Applications using wireless sensor networks and machine-to-machine connectivity now have to depend on battery power in form factors that are small enough to fit in such designs, but which deliver sufficient energy.
The mad rush toward a ubiquitously connected and wireless Internet of Things has not helped, even though it has generated considerable research in how energy harvesting from solar, heat, vibration, and other ambient sources that can be used to power such designs. Almost every technical paper and report I have read about the Internet of Things has as its subtext the challenges of powering such wireless devices over years and decades, and doing so predictably and reliably. Some recent such articles and commentary include:
Building power-efficient CoAP devices for cellular networks
Low-power Interoperability for the IPv6-based Internet of Things
Open WSN standards-based low-power wireless development
Emerging techniques for long lived wireless sensor networks
Efficient supercapacitors for extended lifetime wireless sensor nodes
It will be a while before such sources become practical, and until then embedded developers are stuck with such things as the familiar - and small - coin cell batteries. And, while a whole new generation of coin cell alternatives have emerged, as well as the "micro-power" MCUs that their builders say will operate over years, embedded developers have two challenges: first specifying that the MCUs they get from the vendors actually work at the voltage, current, and power values the data sheets say they do, and second, making sure the batteries they use operate reliably over a range of conditions.
Increasingly frustrated by his inability to answer those questions to his satisfaction, a year ago Embedded.com's Jack Ganssle started reporting on his efforts to pin down and eliminate such uncertainties in his Break Point blogs, starting with "A sneak preview" in which he described the laboratory setup and tools he had gathered together, as well as his motivations:
"I've been running experiments for 6 months to gain a deeper understanding about building ultra-long-lived battery-powered systems," he wrote. "Some of my experiments are quantifying the behavior of the components we use. For instance, there's very little known about how a CR2032 discharges in these ultra-low-sleep current applications, and I've amassed a vast amount of data using some custom tools. The results are surprising, and lead me to doubt that even a ten year life is attainable in a real system."
Since then he has reported regularly on his investigations in his blogs, some of which have been included in this week’s Tech Focus Newsletter, along with a number of other recent design articles and technical papers on battery management and characterization.
Not only will this rigorously low power - and connected - environment we are now in require looking at new approaches to embedded design, it means going back and looking at how to use existing tools and building blocks better. In addition to "Optimizing embedded software for power efficiency," a four-part series debuting on Embedded.com this week, my Editor's Top Picks of recent articles on power management tools and techniques are:
The importance of low power sensing for the Internet of Things
Selecting the right battery for your embedded application
Low-power MCU benchmarking - what datasheets don’t tell you
Understanding MCU sleep modes and energy savings
Eventually harvesting techniques will become reliable enough to be used in embedded designs, and many of the tools and techniques for MCU performance and precise voltage, current and power measurements will find use here as well. But which ones? Another question: will harvesting alone be sufficient or will such designs always be dependent at least in part on batteries?
For answers to such questions, I will depend as always on contributions of ideas, resources, and design articles and blogs from embedded developers. I look forward to hearing from you.
Embedded.com Site Editor Bernard Cole is also editor of the twice-a-week Embedded.com newsletters as well as a partner in the TechRite Associates editorial services consultancy. He welcomes your feedback. Send an email to firstname.lastname@example.org, or call 928-525-9087.