Roberto Canegallo
Laboratorio congiunto STMicroelectronics - ARCES Bologna

Experiences of an autonomous wireless sensor and actuator network (WSAN) in IoT domotic application

This work describes the project of a WSAN made up of autonomous sensor and actuator nodes for a domotic application.
The Internet of Things (IoT) nodes are composed of a low-power microcontroller, a sub-GHz radio for data communication, a power management unit with indoor photovoltaic (PV) or thermoelectric (TEG) transducer for energy harvesting, rechargeable battery, sensor devices and/or actuators. Connectivity between nodes and the network gateway is provided by DASH7, a low-power open source protocol that supports two communication models: the pull model for query-response method (e.g. smart heating) and the push model for data transfer initiated from the nodes (e.g. sensor alarms).
The WSAN experiences two different tasks: smart heating control and water flood sensing. The first consists of temperature sensing node supplied by indoor PV harvester and actuating node, supplied by TEG harvester connected to hot pipe of the radiator, that drive a brushed DC motor connected to the radiator valve. The second consists of water flood sensing node and an actuating node driving a brushed DC motor connected to the water supply system to cut off water flux, both supplied by indoor PV harvesters. To ensure the self-sustainability of the nodes, the average energy harvested has to be greater than the average energy consumed. Experimental results show that, with an illuminance level of 300 lx and a temperature gap of about 10 °C between hot water pipe and environment, the first application is self-sustaining if the temperature is sampled every 7 minutes and the radiator valve is controlled every 19 (8) minutes if valve setting change is kept below 25 % (10 %) of its full range. The second application is self-sustaining, i.e. is able to detect and react to water flood, with 150 lx of illuminance level. Both applications demonstrate how an autonomous WSAN for domestic use is implemented using energy available in the environment.