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Before providing a detailed explanation of each component of SENNO (SENsor Node), we first introduce the principle and characteristics of the chemical gas sensors mounted on our sensor board. The U.S. Environmental Protection Agency (EPA) designates a standardized air pollution level indicator, the Air Quality Index (AQI), which mainly refers as main parameters (together with particulate matter (PM) and carbon dioxide (CO2)) to carbon monoxide (CO), nitrogen dioxide (NO2), and sulfur dioxide (SO2) [9,10]. A monitoring system should be able to detect these noxious gases in a timely and accurate manner. The primary goal of our system is to build an air quality-monitoring tool that measures the above mentioned pollutants with inexpensive compact sensors. Several types of off-the-shelf chemical gas sensors exist, but each sensor has different operation principles. The size, accuracy, and power consumption of a compact gas sensor all vary with sensor type. With the use of electrochemical technology, this type of sensor features both a small size and a fast response time [xxx]. Moreover electrochemical sensors offer several advantages for instruments that detect or measure the concentration of many toxic gases. Most sensors are gas specific and have usable resolutions under one part per million (ppm) of gas concentration matching the EPA requirements. They operate with very small amounts of current, making them well-suited in self-powered wireless nodes. In our project we have adopted the following electrochemical sensors: NE4-CO Carbon monoxide, Nitrogen dioxide NE4-NO2, NE4-NO Nitrogen monoxide, NE4-H2S Hydrogen Sulphide and NE44-NH3 Ammonia from NEMOTO (examples of the sensors adopted integrated in the PCBs are reported in Figure 1 ... ... middle of paper ... ... (ratio adopted 1:100) to create an ultralow input voltage step-up DC/DC converter and power manager that can operate from input voltages of either polarity. This capability enables energy harvesting from thermoelectric generators (TEGs) in applications where the temperature differential across the TEG may be of either (or unknown) polarity. This function covers automatically, imagining SENNO stacked to a window, the cases of external ambient temperatures greater or lower with respect the indoor room temperature where the device is deployed. The energy converter manages the charging and regulation of multiple outputs in a system in which the average power draw is very low, but where periodic pulses of higher load current may be required. This approch is crucial where the quiescent power draw is extremely low most of the time, except for 433 MHz transmit pulses when

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