ENERGY-HARVEST-RD(#3): RF Sensor Node, Solar Power

The purpose of this reference design is to demonstrate an ultra low power wireless sensor, powered from an energy harvesting source. This application is typical of systems which wake periodically to measure and transmit results. Since it is powered from an energy harvesting source, no batteries need to be replaced for the life of the system (life expectancy is greater than 15 years or 7000 mA-H) and the wireless node can be designed with a very thin profile (battery height is 0.17 mm).

The system consists of two components: a wireless Sensor node and an EZRadioPRO® USB Dongle. The Sensor Node uses a Silicon Labs Si1012 wireless MCU. The Dongle uses a Silicon Labs C8051F342 MCU and a Silicon Labs Si4431 radio.

The Sensor Node operates at 919.84 MHz and is powered by a solar energy harvesting power supply. When the wireless Sensor Node is not transmitting data, the Si1012 wireless MCU can remain in a low-power state where it only consumes 50 nA. The leakage current of the energy harvesting supply, when enabled, is approximately 3 µA and is cancelled out by as little as 50 lux shining into the solar cell. This allows the energy harvesting supply to power the system for approximately 7 days in a dark closet (in the ON position) or indefinitely if there is a periodic light source that replenishes the lost energy. The system works both in indoor lighting (200 lx) and outdoor lighting (10,000 lx) conditions.