SOLAR POWERED WIRELESS SENSOR NODE: A DESIGN, IMPLEMENTATION AND ENERGY OPTIMIZATION ANALYSIS

Abstract

The design of an autonomously powered wireless sensor node using solar cells has been proposed. The paper described solar energy harvesting system that employs two energy storage devices (super capacitor and battery) to realize a long-lasting wireless sensor node. The solar energy from the solar panel charge the super capacitor while supplying the sensor node and charge the battery when super capacitor is fully charged or when the input current is sufficiently high. In the absence of solar energy the two energy storage devices handle the sensor node alternatively through a switching circuit called power multiplexer (TPS2113A). To extract the maximum solar panel output at all times, LDO03C dc-dc converter was employed at the input. To optimize energy in the system the radio transceiver was configured to transmit data at the lowest power level (-7dBm) and moderate transmission speed (9600bps) as well as using sleep mode for both transceiver and microcontroller. This way the current consumption of the sensor node reduced from the range of 95-100mA to the range of 55-60mA. At the lowest transmitting power the temperature/humidity data was successfully transmitted and received at a distance up to 100 metres with line of sight (LOS) and up to 40 meter without LOS. The energy storage devices were able to power the sensor node successfully from sunset to sunrise.