An Energy-Autonomous and Maintenance-Free Wireless Sensor Platform with LoRa Connectivity

Wireless sensor nodes (WSNs) are typically powered by batteries, which results in a maintenance burden and cost, especially in Internet of Things (IoT) scenarios that install many devices. For these applications, the ideal node must be set-and-forget, maintenance-free, and low-cost. This paper proposes a self-powered wireless sensor platform, implemented through a photovoltaic cell and with LoRa connectivity. An off-the-shelf amorphous silicon photovoltaic cell of 58.1 mm$\times 48.6$mm is used to harvest and sense indoor ambient light with a limit of detection of 200 lux. The system embeds a 2 mF storage capacitor that every cycle stores enough energy to send a maximum of 30 bytes data packet when the LoRa transmitter is configured with a spreading factor of 7, a bandwidth of 125 KHz, and an output transmitted power of 14 dBm. Experimental measurements performed in an urban area have shown that a 20 bytes data packet is received correctly and reliably at the maximum distance of 560 m.