RF-Powered Wireless Sensors

An interesting project we’ve been working on is to power the Texas Instruments eZ430-RF2500 wireless sensor demo system.  The components are easy to set-up and use, and the RF2500T target board has very low power consumption.  The RF2500T modules use TI’s MSP430 microcontroller, a Chipcon radio, and the SimpliciTI protocol.

We powered the RF2500T Target Board without batteries using a 900MHz transmitter and lab boards with a Powerharvester(TM) module.  The capacitor on the receiving board (shown above left) was first charged to 3V and then the sensor was activated.  The sensor would then run continuously as wireless power was available, and then until the capacitor voltage dropped below the operating threshold.

Later, we used one of the “charge and fire” lab boards from the Lifetime Power(TM) Evaluation and Development Kit (shown above right) to automate the operation.  The P2100 Powerharvester module on the lab board is designed to convert RF energy and store it in a capacitor.  When a voltage threshold is reached on the capacitor, the P2100 switches on its’ output to the sensor at 3.3 volts.  When a lower voltage threshold is reach on the capacitor the output to the sensor is switched off.  The power output to the wireless sensor can be continuous if the received power is greater than the power consumption of the sensor, or the sensor can be operated intermittently when enough energy is accumulated in the capacitor.

The ability for a sensor to support intermittent operation, with variable inactive periods or long sleep periods, and with minimal start-up sequencing and communications handshaking, will provide the farthest range with RF energy harvesting.