The market for energy harvesting devices is expected to grow exponentially this decade. IDTechEx forecasts that more than ten billion energy harvesting devices will ship by 2019 - a 20x increase over the roughly 500 million units that shipped in 2009.
Although systems powered by harvested energy sources have existed for many years, developers have been challenged to implement wireless sensor nodes within very low power budgets. Silicon Labs claims it has met this design challenge by creating a wireless energy harvesting system based on its Si10xx wireless microcontroller (MCU) family.
Silicon Labs' energy harvesting reference design includes wireless network and USB software and a complete circuit design with RF layout, bill of materials (BOM), schematics and Gerber files.
The design includes a solar-powered wireless sensor node that measures temperature, light level and charge level, using an Si10xx wireless MCU to control the sensor system and transmit data wirelessly and a thin-film battery to store harvested energy. A wireless USB adapter that connects the wireless sensor node to a PC for displaying sensor data is also featured, using Silicon Labs' Si4431 EZRadioPRO transceiver with an MCU running USB-HID class software and EZMac wireless software stack. In addition, a wireless sensor network GUI displays data from up to four sensor nodes.
The thin film battery used in the energy harvesting reference design has a capacity of 0.7 mAh. In direct sunlight, the battery can be recharged fully in only two hours. While in sleep mode, the wireless sensor node will retain a charge for 7,000 hours. If the wireless system is transmitting continuously, it will operate non-stop for about three hours, although it is designed to constantly recharge itself at an appropriate level to keep the thin-film battery from completely discharging.
Silicon Labs' energy harvesting reference design accommodates a wide range of harvested energy sources. An on-board bypass connector gives developers the flexibility to bypass the solar cell and tap other