Bluetooth Low-Energy Sensor Node For Gas Monitoring

The capability of measuring the concentration of gaseous analytes is of interest in different areas, from industrial safety to environmental monitoring. A wide variety of gasses is present in the atmosphere, produced both by industrial and natural processes. Their constant monitoring helps to prevent and analyze their effects on people, on the natural environment and on materials. The constant presence of polluting agents in urban areas promotes the interest in monitoring the indoor air quality inside workplaces, homes and public areas. For example, carbon monoxide and nitrogen oxides, generated in hydrocarbons combustion processes, are widely present in metropolitan locations. Moreover, several industrial processes imply the production of toxic gasses. In such cases a continuous monitoring of the factory environment is mandatory in order to prevent harmful situations. For example, the hydrogen sulfide, an extremely dangerous agent, is a waste product for the food industry, coke production, leather tanning industry and many others. The effects of toxic gasses on humans and animals are both of long and short term. Most of them directly involve the respiratory tract, eyesight and the neural system. Also plants and crops are negatively affected by such gasses causing land degradation. Moreover, their effect is also visible on monuments and buildings. The purpose of this work is to design a measurement system capable of performing environmental monitoring of a wide variety of gas in indoor locations where a cabled network would be of difficult installation and a constant maintenance not possible. In particular, the system should be included into an existing wireless environmental monitoring sensor network, developed during past years at Polytechnic of Turin, whose nodes are capable to operate for several years without attendance. This wireless network is currently composed by battery powered Bluetooth nodes that can measure temperature and humidity and that are designed to work in conditions where neither a continuous power source nor a continuous Internet connection are present. These features require the use of a low power architecture capable of both wirelessly transmitting and storing all the produced data into an internal memory. The gas sensor node should therefore be able as well to operate as data-logger and as wireless Bluetooth low-energy node. The wide variety of aeriform polluting agents encourages the development of a system capable of detecting as many different gaseous analytes as possible, where their concentration can be dangerous with a prolonged exposure. The work started with the investigation of the available gas sensing technologies suitable for the development of the system. The characteristics of each sensor, for each considered type of gas, has been compared analyzing the impact on the system's performances. After this preliminary step the work focused on the design of a measurement system capable of functioning with all the selected sensors, making particular attention to the power consumption of every component present in it, to comply with the severe power requirements. During the design an appropriate micro-controller optimized for Bluetooth low-energy transmission has been chosen and the firmware has been developed to correctly control all the components and take measurements from the sensor. Subsequently the Bluetooth wireless transmission has been addressed taking particular care to the radio power consumptio