Toward Maintenance-Free IoT Sensor Nodes: An Energy-Harvesting Wireless Platform Based on STM32WL55 With Sub-GHz LoRaWAN Connectivity

The rapid growth of Internet of Things (IoT) applications increases the need for wireless sensor nodes that support maintenance-free long-term operation. This article describes a fully energy-autonomous wireless sensor platform based on the STM32WL55 microcontroller unit (MCU), featuring integrated sub-GHz LoRaWAN connectivity and power management. The system uses a photovoltaic cell for energy harvesting and ambient light sensing. An embedded finite state machine manages and optimizes sensing and communication tasks. A 1.2 F supercapacitor provides energy backup, enabling up to 12 hours of autonomous operation with 15-minute transmission intervals. Experimental results demonstrate continuous environmental sensing and long-range communication powered exclusively by harvested energy. The average power consumption is below 50 μW, and the communication range is approximately 1 km. This platform provides a scalable, environmentally friendly, and maintenance-free solution for sustainable IoT deployments.