Green Power specifications opens up wireless energy harvesting in the smart home

Paul Boughton

A ZigBee PRO specification, Green Power, is supporting low cost energy harvesting and ultra-long battery life for ZigBee wireless applications. Nick Flaherty reports.

A new ZigBee PRO specification called Green Power is now supporting low cost energy harvesting and ultra-long battery life for ZigBee wireless applications for the Smart Home, while an industry group is looking to benchmark ultra-low power devices.

The Green Power feature in Zigbee PRO 2012 gives battery-free, energy-harvesting devices the ability to join any Green Power- enabled ZigBee network.

Without requiring batteries, the self-supporting devices typically harvest just enough power themselves to communicate a brief command from mechanical, thermal or RF energy. [Page Break]

For example, a light switch without a battery harvests energy from flipping the switch on or off. This energy is captured to send the 'on' or 'off' command to the network to switch on or off the appropriate light and so the self-powered light switch can be located anywhere in the room without a need for running power wires.

One of the first devices to support the new standard, and one of the ‘golden units’ used for testing is the GP410 Green Power controller from Dutch low power wireless chip designers GreenPeak Technologies. This is a fully integrated system-on-chip solution for power harvesting end nodes for light switches, smart home devices, or for applications designed to run on a single battery for many years.[Page Break]

The GP410 integrates a radio transmitter, real-time Medium Access Control (MAC) processor, a security engine and a harvester interface and the ultra-low power consumption ensures that multiple (redundant) packets can be transmitted with a small harvester or tiny battery. The GP410 is designed to support both bursting and trickling energy harvesters and is therefore well suited to energy harvested from flipping a light switch as well as solar powered sensors.

The integrated features simplify design complexity. Developers can design low cost light switch products by using simple PCB antennas that require no shielding. No additional components, such as a voltage converter, are required to design a self-powered end node.[Page Break]

“GreenPeak is one of the first ZigBee Alliance members to offer Green Power products, and as Vice Chair of the Green Power working group, GreenPeak has been one of the driving forces and an influential contributor in establishing the Green Power feature,” said Cees Links, founder and CEO of GreenPeak Technologies. “The GP410 enables our customers to quickly develop and easily deploy low cost, battery-free, self-powered solutions, the ultimate maintenance-free Smart Home end-devices. Green Power nodes can also be powered by a small battery, and due to the ultra-low power consumption, the battery will easily outlast the application’s expected life span. The high level of integration of the GP410 makes it easy to design and develop low-cost, light switches and other self-powered Smart Home applications.”

The EEMBC benchmarking organisation is also looking at the same ultra low power market to find a standard way to quantify the real world power consumption of such devices in applications such as portable medical devices, security systems, building automation, smart metering, and also applications using energy harvesting devices. [Page Break]

The new benchmark will initially look at the power used when a controller moves from running to its real time clock sleep mode. New benchmarking code will be required as the standard CoreMark benchmarks use too much power, says Horst Diewald, chief architect of MSP430 Microcontrollers at Texas Instruments (TI) in Germany who is chair of the EEMBC ULP working group.

“We have seen a significant need for a well-constructed, industry-accepted benchmark to equitably evaluate the energy efficiency of microcontrollers,” said Diewald. “Unfortunately, the application developer cannot rely on datasheet parameters alone to compare total Microcontroller power consumption and select an appropriate microcontroller.”

The first benchmark should be available by the end of March to assess different controllers. Members of the group include Analog Devices, ARM, Atmel, Cypress, Energy Micro, Freescale, Fujitsu, Microchip, Renesas, Silicon Labs, STMicro and TI, although some notable energy harvesting device developers are missing.

The benchmarking methodology will allow the Microcontrollers to enter into their idle or sleep modes during the majority of time when they are not executing code, thereby simulating a real-world environment where products must support battery life measured in months, years, and even decades.