# Real-Time Monitoring of Indoor Air Quality with Internet of Things-Based E-Nose
## 3 Materials and Methods
The electronic features of the sensors used in the IoT-based e-nose system are given in Table 1.  
The images of the IoT-based e-nose system used in air quality measurements and formed from different sensors are displayed in Figure 2. The sensors used in the system are mounted in a \(17\times 12\times 8\) cm size sealed box per the measurement specifications. In addition to the sensors used for measurement, the box includes a printed circuit board, a fan for airflow to the dust sensor, and a power supply for the energy of the system. The measurement system can work with a 12 V DC adapter, and additionally has a mobile use feature when paired with a power bank that can be connected to the 5 V DC USB port. This feature provides a great advantage for short-term measurements. When supplied from a 5 V power supply, the measuring device draws a current of 160 mA. With a 5000 mAh power bank, it has a measuring time of approximately 30 h. Using a wireless internet connection, it provides the opportunity to measure air quality from many common living areas such as parks, gardens, highways, industrial areas, sports fields, public transportation, cafes, restaurants, schools, hospitals. The climate parameters and gas concentrations are a median of 12 measurements taken at 5 s intervals. This minimizes the effect of erroneous measurements brought about by faulty sensors. Users are notified by exceeding the designated gas concentration and climate parameter thresholds. Five-minute averages are calculated and delivered to users as notifications, preventing false warnings that may mislead users. In this e-nose system which measures air quality, no memory element is used for data recording. The received data are recorded directly to the Blynk cloud server via the mobile interface. The data are sent to the registered e-mail address of the user when requested. The status of the internet connection is checked before each data transmission. When not connected, data packets \begin{table}
\begin{tabular}{c c c c} \hline \hline
**ID** & **Equipment Name** & **Types** & **Electronic Features** \\ \hline \multirow{2}{*}{1} & \multirow{2}{*}{CO\({}_{2}\) gas sensor} & MH-Z14 & Detection range 0–10000 ppm; operating voltage: 4–6 V; accuracy: \(\pm\) 50 ppm \(\pm\)5\%; resolution: 5 ppm; output Voltage: 0.4–2 V; operating temperature: 0–50 °C \\ \hline \multirow{2}{*}{2} & \multirow{2}{*}{NO\({}_{2}\), CO gas sensor} & MICS-4514 & Detection range 1–1000 ppm (CO); 0.05–5 ppm (NO\({}_{2}\)); operating voltage: 4.9–5.1 V; operating temperature: \(\sim\)35–85 °C; heating current: 58 mA \\ \hline \multirow{2}{*}{3} & \multirow{2}{*}{Dust sensor} & GP2Y1010 AU & Operating voltage: 5 V; output voltage: 0.9 (no dust)–3.4 V; operating current: max 20 mA; operating temperature: \(\sim\)10 to 65 °C, accuracy \(\pm\)15\% \\ \hline \multirow{2}{*}{4} & \multirow{2}{*}{Temperature and Humidity sensor} & \multirow{2}{*}{DHT22} & Temperature range: \(\sim\)40 °C to 80 °C; humidity range: 0\% to 100\%; operating voltage: 3.5–5.5 V; operating current: 60 uA; output: serial; resolution: 0.1 °C and \(\pm\)1 rH\%; accuracy: \(\pm\)0.5 °C and \(\pm\)1 rH\%; resolution: Temperature and humidity are 16-bit. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Electronic features of the sensors in the IoT-based e-nose measuring system. Figure 2: Images of the IoT-based e-nose system. that cannot be temporarily transmitted are stored to ensure data integrity, and then, when the internet connection is re-established, these packets are sent to the cloud server using past time tags. In this way, data loss can be prevented by providing continuity in the data flow. The front panel images of the developed Android-based mobile user interface are given in Figure 3. Control over mobile devices in IoT applications has become very common. There are many free options available for Android and iOS devices.