Energy Autonomous Wireless Sensing Node Working at 5 Lux from a 4 cm2 Solar Cell

Abstract

Harvesting energy for IoT nodes in places that are permanently poorly lit is important, as many such places exist in buildings and other locations. The need for energy-autonomous devices working in such environments has so far received little attention. This work reports the design and test results of an energy-autonomous sensor node powered solely by solar cells. The system can cold-start and run in low light conditions (in this case 20 lux and below, using white LEDs as light sources). Four solar cells of 1 cm2 each are used, yielding a total active surface of 4 cm2. The system includes a capacitive sensor that acts as a touch detector, a crystal-accurate real-time clock (RTC), and a Cortex-M3-compatible microcontroller integrating a Bluetooth Low Energy radio (BLE) and the necessary stack for communication. A capacitor of 100 μF is used as energy storage. A low-power comparator monitors the level of the energy storage and powers up the system. The combination of the RTC and touch sensor enables the MCU load to be powered up periodically or using an asynchronous user touch activity. First tests have shown that the system can perform the basic work of cold-starting, sensing, and transmitting frames at +0 dBm, at illuminances as low as 5 lux. Harvesting starts earlier, meaning that the potential for full function below 5 lux is present. The system has also been tested with other light sources. The comparator is a test chip developed for energy harvesting. Other elements are off-the-shelf components. The use of commercially available devices, the reduced number of parts, and the absence of complex storage elements enable a small node to be built in the future, for use in constantly or intermittently poorly lit places.

A Citizen Science Tool Based on an Energy Autonomous Embedded System with Environmental Sensors and Hyperspectral Imaging

“…Similar systems are very prevalent in the literature for Smart Agriculture applications, incorporating data acquisition from on-board sensors and processing at the edge, such as La Rosa et al ( 2022) [52]. The groundwork for the power management architecture of the SES used in this paper was explored by Meli et al (2023) [53], where the design of an energy autonomous low-power BLE node was described, capable of working under an illuminance as low as 5 lux. This is the first time that this system is used for autonomous decision-making on the edge, in the context of Smart Agriculture.…”

Toward Indoor Simulations of OPV Cells for Visible Light Communication and Energy Harvesting

“…In [45], the authors developed a full autonomous indoor WSN by employing a 5.81 cm × 4.86 cm amorphous silicon (𝛼-Si) PV cell, considering a constant 200 lux illumination (generating around 137.1 𝜇W) to design the circuit. Finally, Meli et al developed an autonomous sensor node operating at incredibly low illuminances (5 lux) [46]. The system, associated to energy management strategies, supplied a touch detector, a real-time clock and a microcontroller with four 98 mm² PV cells.…”

Green and Sustainable Industrial Internet of Things Systems Leveraging Wake-Up Radio to Enable On-Demand IoT Communication

“…Alternatively, some solutions use ambient energy through photo-voltaic cells or ambient RF energy, providing the advantage of not requiring any additional transceiver. Even indoor harvesting is possible, depending on the existing ceiling light, which has very low illuminance requirements [35].…”