An Indoor Smart Farm Sensor Node with Energy Harvesting System

In smart farm applications, wireless sensor nodes (WSN) are used for monitoring environmental parameters. However, their batteries have to be replaced manually every time they run out of charge: a time-consuming process, especially if the WSNs are not easily accessible. Thus, we developed a batteryless WSN based on the LPSTK-CC1352R SensorTag for an indoor hydroponic farm. Ultra low-power operation was achieved after various software tweaks, enabling a current draw of only 8 $\mu$A in between transmissions. We also designed a small-scale energy harvesting device that can extract energy from the LED grow lights in the farm. It is composed of an SM141K06LV monocrystalline PV cell, a BQ25570 boost charger and buck converter, and a 220 mF supercapacitor for energy storage. An energy-aware algorithm was also developed based on battery monitoring and event-based transmission. By dynamically adjusting the WSN’s transmission rate based on available energy, the WSN was able to last 1.5 hours more or 40% longer than with a constant 1-minute transmission rate. This optimization also makes the WSN more autonomous and adaptable to any lighting schedule with at most 5 hours of darkness.