Thermoharvester-driven wireless sensor node enables battery-free operation

Freiburg, Germany — Micropelt GmbH claims to offer the world's first commercially available thermo-powered wireless sensor system, the TE-Power NODE. The company's built-in chip thermogenerator takes a few degrees of temperature differential and harvests that thermal energy to operate the wireless sensor node, enabling unlimited battery-free operation.

Wireless sensor networks offer many advantages. Market growth, however, lags behind expectations as many potential users avoid the burden of having to maintain hundreds or thousands of batteries.

Also available is the TE-Power NODE evaluation kit, which transmits multiple channels of digital sensor data helping both users and integrators of thermoharvesters better understand many aspects of their implementation in terms of application scenarios and energy budgets.

The TE-Power NODE consists of a 60 by 27 mm footprint aluminum base plate that carries up to two Micropelt MPG-D751 thermogenerators, allowing the energy supply to be scaled for the amount needed by the designated application. An aluminum heat spreader is mounted on top of the thermogenerators and is stabilized and insulated by a PCB which also holds the receptacles for various plug-on modules. The heat spreader features threaded holes for accessing various heat sinks with minimal effort, allowing for detailed exploration of the device's thermal path and easy repair.

To convert the variable incoming thermo-voltage into a battery-like constant voltage, the original TE-Power PLUS DC/DC converter was modified to supply a constant 2.4 V and to charge a 100 microfarad (F) capacitor to feed the duty cycle of the accompanying pluggable wireless system.

The company's evaluation kit uses widely accepted ultra-low-power technology from Texas Instruments (TI), supporting both IEEE 802.15.4 compliant and custom solutions.

To operate the wireless sensor node, it must be attached to a suitable heat source. After a few seconds the TE-Power NODE begins transmitting information to a PC via TI's standard eZ430-RF2500 USB receiver module. Within as little as 2 milliseconds a minimized stack protocol transmits the temperature of the thermogenerator's hot and cold sides once every second along with the respective operating voltage. An additional I2C standard based digital sensor interface provides a channel for optional transmission of data such as vibration or pressure values. The information is displayed on the PC such that users can easily assess the quality and consistency of the thermal power supply.

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