Saturday, June 21, 2014

Microcontrollers: Batteries Not Included. Or Needed.

The concept of energy-harvesting or energy-scavenging devices is intriguing to me. If the power for an electronic component or computing device comes from energy harvesting, you don't need to plug it in and you don't need batteries to power it.

Wikipedia defines energy harvesting as:
"Energy harvesting (also known as power harvesting or energy scavenging) is the process by which energy is derived from external sources (e.g. solar power, thermal energy, wind energy, salinity gradients, and kinetic energy), captured, and stored for small, wireless autonomous devices, like those used in wearable electronics and wireless sensor networks."
The concept of energy harvesting somewhat applies to the larger field of capturing needed energy from the immediate environment of the item that will use the energy. Examples of this larger definition include:
  • Regenerative braking, which converts kinetic energy of a vehicle into a stored energy form, such as a flywheel or battery, which can later be used to provide power to the vehicle.
  • Mobile items with solar cells, such as a car with solar cells on the roof that help keep the car cooled when it's parked in the sun, or the Soar Impulse aircraft (shown at right) that uses solar power it captures to both gain altitude (potential energy) and to charge its batteries during the day, then uses the altitude and batteries to keep itself flying through the night.
In terms of energy harvesting for microcontrollers (MCUs), a VentureBeat article, "Spansion goes battery-less with tiny ‘Internet of things’ chips," talks about two Spansion energy harvesting chips, MB39C811 and MB39C831, which can power MCUs. Spansion sees energy harvesting as one alternative for powering the Internet of Things (IoT).
"Spansion says it can eliminate the need to put a battery in the tiny sensors that will deliver the measurements from the Internet of things.” That should make it much more affordable to deploy billions of such sensors...By getting rid of the battery, such chips...will lower the maintenance costs significantly for companies that deploy networks of sensors for Internet of things applications...Spansion’s chips include a family of power management integrated circuits that can capture and store energy from ambient sources. Those include solar, piezoelectric (vibration), and temperature changes (Peltier). It could also use energy from electromagnetic induction."
An industrial use case for this combination of energy harvesting and low-power electronics is wireless sensor networks in large manufacturing facilities. Manufacturing equipment often generates vibration or heat, both of which can be used to power the sensor electronics and wireless communications systems. Had the US economy not crashed in 2007 / 2008, I quite possibly have been an engineer for a small startup that was going to install custom designed energy-harvesting wireless process sensor networks in aluminum smelters around the world. Aluminum production facilities are very large, so lots of money can be saved by not having to run process sensor powere and communications wiring throughout the facility. The recession caused the aluminum manufacturers and the startup company to put the project on hold for several years.

A potential application for energy-harvesting electronics like the Spansion chips mentioned above would be an agricultural monitoring system that has sensors spread out over several fields and greenhouses with a wireless communication system for getting the sensor data to collection nodes and to a central data storage and processing location. The energy harvesting means that power lines don't need to be installed to every sensor point and communication wiring doesn't need to be run to all the wireless modules. Energy harvesting powers the sensor electronics and the wireless communications electronics.

MCUs that would work well for this application are the sensor hub microcontrollers mentioned in yesterday's blog post, "Microcontrollers And Sensor Hubs," such as the Atmel SAM G microcontrollers. The SAM Gs are only 3 x 3 mm, and they use less than 7 µA in deep sleep with SRAM retention.

Although I can't immediately think of a Humboldt short term microcontroller application that requires energy harvesting, it would be interesting and educational to design and build a Humboldt Microcontrollers Group project that includes energy harvesting. And once we have familiarity with the energy harvesting circuits and the low-power devices that can be powered by the ambient energy that is collected, we may find financially viable applications, either in Humboldt County or elsewhere in the world.


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