A Battery-free and Sensor-less Photovoltaic Tag for Real-time Indoor Light Illuminance Evaluation

Cheng Tian, Zijie Chen, Junrui Liang

Abstract: As the number of Internet of Things (IoT) nodes exponentially increases, replacing or recharging batteries for these end devices limits the working lifetime and space span of ubiquitous IoT. This paper introduces a battery-free IoT tag for indoor light illuminance estimation and evaluation. Utilizing the relationship between the light intensity and the interval between transmitted Bluetooth low energy (BLE) packets, the proposed system assesses the current indoor lighting conditions without using an additional sensor. Owing to their battery-free characteristics, these maintenance-free tags can be easily installed in a very wide range. The cost of this proposed tag is low, only a few discrete components enable the energy to slowly buffer and rapidly release after fully charged. The on/off voltage thresholds can be handily reconfigured. The compact prototype, whose size and cost are only 32x20 mm2 and US$1, respectively, is fabricated and tested. It is capable of grading light levels above 30 lux. Field tests prove the feasibility and performance of this design. It gives a new insight into the future of pervasive sensing.