With its promise of battery-less operation, energy harvesting offers an attractive solution for powering smart devices in the Internet of Things (IoT). Despite its apparent simplicity, however, a power supply capable of drawing useable energy from ambient sources presents multiple challenges. For designers new to energy harvesting, as well as those experienced in its intricacies, development efforts can gain a quick boost through the use of energy-harvesting kits from manufacturers including Advanced Linear Devices
, Linear Technology
, Maxim Integrated
, Microchip Technology
, Mide Technology
, Silicon Labs
, Texas Instruments
and Wurth Electronics
A robust energy-harvesting supply provides an extensive range of functionality (Figure 1). On the input side, transducer interface circuitry needs to maintain the transducer at its maximum power point; employing sophisticated maximum- power-point tracking (MPPT) algorithms to maintain optimum-energy conversion. Within the subsystem, energy-management circuitry needs to ensure proper charge and discharge cycles of energy-storage devices, such as supercapacitors and thin-film batteries.
Figure 1: Simple in concept but difficult in execution, energy-harvesting power supply design presents significant challenges for ensuring maximum energy conversion and efficient power management (Courtesy of the Next-Generation Energy-Harvesting Electronics, Engineering and Physical Sciences Research Council).
On the output side, power-management circuitry needs to ensure proper supply levels to the load and gracefully shut down load circuitry if harvest energy and stored power fall below minimum levels. In turn, those circuits need to restore the supply in the correct sequence needed to prevent mid-reset collapse of load circuitry due to insufficient power. In short, energy-harvesting requires strict attention to every detail of energy conversion and power management, and can threaten to stall tight schedules for IoT device design.
Evaluating energy-harvesting components
Energy-harvesting development kits provide a complete, tested solution typically built around one of a number of specialized energy-harvesting ICs and components and designed to showcase that part's capabilities. One class of demo boards offers engineers an opportunity to explore components such as storage devices and energy transducers. For example, thin-film battery maker Cymbet offers its CBC-EVAL-12
kits for evaluation of its real-time clock (RTC) chips with integrated power backup based on its EnerChip rechargeable storage device technology.
Mide Technology simplifies evaluation of its piezoelectric transducers with its EHE004
board, which is designed to connect directly to any Mide Volture
piezoelectric device. The board includes a conditioning circuit comprising a full-wave rectifier feeding a Linear Technology LTC3588-1
piezoelectric charge management IC to maximize total piezoelectric energy harvester output (Figure 2).
Figure 2: The Mide Technology EHE004 development board provides a complete energy-harvesting conversion circuit based on the Linear Technology LTC3588 charge management IC (Courtesy of Mide Technology).
Another class of demo boards helps engineers explore the performance characteristics of specialized power-management ICs built for energy-harvesting applications. For example, engineers can also evaluate the Linear LTC3588 directly using Linear's own 1459B
demonstration power supply board.
Similarly, the Maxim Integrated MAX17710GB20
Evaluation Kit helps developers gain a quick start in examining energy-harvesting applications built around the Maxim MAX17710GB
energy-harvesting charger and protector IC. The Maxim kit combines a solid-state energy-storage device with a solar cell in a complete energy-harvesting design intended to showcase the MAX17710GB's features.
The STMicroelectronics STEVAL-ISV015V1
demonstration board lets engineers work with an energy-harvesting design built around the ST SPV1040
solar boost converter and ST LD39050
low-voltage LDO regulators. For demonstrations of its own energy-harvesting ICs, Texas Instruments offers its BQ25504EVM
evaluation module for its BQ25504
boost converter and charger IC, while its BQ25570EVM
evaluation board features its BQ25570
power-management IC with boost charger and nanopower buck converter.
MCU-based demo kits
Another class of energy-harvesting kits focuses on demonstrating the use of a particular low-power MCU in energy-harvesting applications. The kits typically combine a third-party energy-harvesting demo board with an MCU evaluation board coupled with a software-development environment.
The Wurth Electronics IC-744885 kit bundles a Silicon Labs EFM32 Giant Gecko
Starter Kit with the Linear Technology Multi-Source Energy Harvester (Figure 3). The SiLabs kit combines SiLabs' Simplicity Studio for software development with a complete demo system board that includes an ARM Cortex M3-based EFM32GG990F1024
32-bit MCU, LCD, 128 kB RAM, 1024 kB Flash, USB, and SEGGER J-Link, as well as additional connectors, LEDs, pushbuttons, and more. The Wurth kit enables engineers to explore energy conversion from multiple ambient sources including solar power, thermoelectric generators (TEGs), piezoelectric devices, and inductive energy.
Figure 3: The Wurth Electronics energy-harvesting development kit bundles a Silicon Labs Giant Gecko kit with a Linear Technology energy-harvester (lower right) capable of generating power from multiple ambient sources (Courtesy of Wurth Electronics).
The Microchip Technology XLP 16-bit Energy Harvesting Development Kit
is intended as a comprehensive-development platform for energy-harvesting application development. Based on Microchip’s PIC24F16KA102 XLP
(eXtreme Low Power) MCU, the main board provides a PICtail connector for adding RF connectivity and comes with the PICkit 3 programmer/debugger for use with Microchip’s free MPLAB Integrated Development Environment. The kit combines the Microchip eval board with a Cymbet solar-energy-harvester board capable of harvesting indoor or outdoor light and storing excess energy in two Cymbet EnerChip thin-ﬁlm rechargeable energy-storage devices.
Silicon Labs features its Si1012
wireless MCU in its Energy-Harvesting Reference Design
. The SiLabs kit provides a complete wireless-sensor node based on the Si1012 and powered by a solar cell built into the board. The SiLabs kit also includes a USB dongle based on the SiLabs EZRadioPRO, allowing developers to connect wirelessly with the sensor node and receive sensor data. For this demonstration, the wireless-node board provides battery level and temperature data from the on-chip temperature sensor. Along with the Silicon Labs Si4431 EZRadioPRO
RF transceiver, the dongle uses a Silicon Labs C8051F342
Texas Instruments showcases its MSP430 MCU series with its MSP430 Solar Energy Harvesting Development Kit
, which is intended as a complete-open-source application with a sample project that can be used to test hardware and even serve as a framework for energy-harvesting projects. Based on TI's MSP430F2274
MCU and CC2500
2.4 GHz wireless transceiver, the kit includes a pair of Cymbet thin-film EnerChip storage devices and a high-efficiency 2.25 x 2.25 in. solar panel optimized for operating indoors under low-intensity fluorescent lights. The kit includes firmware for the MSP430 as well as a PC-demo application to display data samples from the wireless connection.
Manufacturers who offer drop-in modules for energy-harvesting applications also bundle their modules with supporting materials in evaluation kits. For example, the Advanced Linear Devices EH300 kit
features the ALD EH300 energy-harvesting module. The ALD EH4205/EH4295
kit bundles the EH300 with its EH4205 and EH4295 modules designed to boost very-low voltages to useable levels for the EH300.
Building an efficient energy-harvesting power supply offers the promise of battery-less operation, but can present significant challenges in optimizing energy conversion and power management. Energy-harvesting demonstration kits offer ready-made solutions that help engineers new to energy harvesting quickly gain experience; and help experienced energy-harvesting developers accelerate product-development schedules. Using available energy-harvesting kits, engineers can quickly learn how to take advantage of ambient-energy sources for powering IoT devices.
For more information on the kits and parts mentioned in this article, use the links provided to access product information pages on the Digi-Key website.