IoT Sensor Nodes

The ambient parameters inside buildings, like temperature, humidity, and illumination level are valuable information that can be used to optimally control HVAC and lighting systems. Such optimal operation can significantly reduce energy consumption and improve the energy efficiency of buildings. Conventional sensor systems either use batteries or wired power supply. Wired power connections are expensive and limit the mobility and locations where the sensors can be placed. On the other hand, battery powered devices require frequent manual battery changes. Not only do batteries hold the hassle of continuous maintenance, but if not recycled properly, they pose a threat to human health and the environment due to their toxic chemical constituents. This research involves designing and prototyping a self-sustaining batteryless IoT sensor system for indoor environment monitoring suitable for smart building applications. Our designed IoT sensor is self-sustaining which powers itself by harvesting energy from ambient indoor light. Alternatively, it can be powered using a remote infrared laser beam in the absence of ambient light. The built-in energy harvesting circuit integrates a solar cell, a DC/DC converter, and an energy storage capacitor. When the capacitor charges to a certain voltage, the low-power STM32 M0+ microcontroller wakes up and sends sensor readings to a hub. The circuit is designed such that discharge of the capacitor from its charged state gives enough time for the microcontroller to complete sensor reading duties, and then transmit the data using an infrared transmitter to a nearby hub. The Wi-Fi enabled hub then uploads the data collected from all sensors to the cloud, which is then analyzed and can be used to control HVAC, power outlets, and indoor lighting of the building to optimize energy usage. We will present the circuit design, programming strategy, and the communication techniques used to develop this smart building IoT sensor