# Development of Multi-Item Air Quality Monitoring System Based on Real-Time Data
## 3 Results and Discussion
### Hardware Fabrication of Multi-Item Air Quality Monitoring System  
According to the hardware design of 2.2, a multi-atmospheric measuring device was manufactured, and the details are shown in Figure 5. O\({}_{2}\), H\({}_{2}\)S, NH\({}_{3}\), SO\({}_{2}\), NO\({}_{2}\), O\({}_{3}\), and CO sensors are manufactured to fit into one board using the minimum area. The VOC sensor generates heat, so it was installed in a little gap. The temperature and humidity sensor were located next to the vent to avoid interference from the inside generated heat. The particle matter sensor was installed separately below to avoid interference with other sensors. CO\({}_{2}\) and CH\({}_{4}\) sensors were installed on the separate probe rod so that it could be connected to the main device. The fan is designed to maintain proper airflow. The battery, PWSIS2P-7.0A, with a capacity of 7000 Am, was installed inside of the main device. The battery help measuring a device for 24 h without power. The operation step is to press the on/off button to turn on the device; the device then starts measuring all items and transmits the measured data to the server. When the start/stop button is pressed, the measured information is automatically saved to the server and SD card once per minute. The front MODE button is a touch button, and each time it is touch, the value of the currently measured item can be checked sequentially on the front LED display. The sixteen items to be measured are automatically calibrated, but a manual calibration function is installed in the smartphone application to make it more accurate. The calibration function has a very important effect on the accuracy or precision of the measuring instrument [33]. Manual calibration was made with an arithmetic algorithm to obtain a zero-value using standard gas. The communication unit averages the measured data using Bluetooth and Wi-Fi at 1 min intervals and stores the data in the server and SD card. Figure 5 shows the exterior and interior of the manufactured measuring device.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Index** & **Item** & **Unit** & **Normal** & **Bad** & **Very Bad** & **Risk** \\ \hline \multirow{8}{*}{Measurement} & PM\({}_{2.5}\) & \(\mu\)g/m\({}^{3}\) & 0–35 & 36–75 & 76–1000 & Respiratory hazard \\  & PM\({}_{10}\) & \(\mu\)g/m\({}^{3}\) & 0–80 & 81–150 & 151–1000 & Respiratory hazard \\  & CO & ppm & 0.0–9.0 & 9.1–15.0 & 15.1–1000 & Poisoning \\  & CO\({}_{2}\) & ppm & 0–1000 & 1001–3000 & 3001–10,000 & Poisoning \\  & VOCs & ppb & 0–300 & 301–500 & 501–60,000 & Poisoning \\ \cline{1-1}  & O\({}_{2}\) & \% & 19.0–30.0 & 18.9 or less, 30.1 or more & Poisoning \\ \cline{1-1}  & item & H\({}_{2}\)S & ppm & 0–5 & 6–100 & Poisoning \\ \cline{1-1}  & NH\({}_{3}\) & ppm & 0–5 & 6–40 & 41–100 & Poisoning \\ \cline{1-1}  & CH\({}_{4}\) & ppm & 0–140 & 141–50,000 & Explosion Hazard \\ \cline{1-1}  & SO\({}_{2}\) & ppm & 0.0–0.1 & 0.2–20.0 & Poisoning \\ \cline{1-1}  & NO\({}_{2}\) & ppm & 0.0–0.1 & 0.2–20.0 & Poisoning \\ \cline{1-1}  & O\({}_{3}\) & ppm & 0.0 & 0.1–0.15 & 0.16–20.0 & Poisoning \\ \hline \hline \end{tabular}
\end{table}
Table 2: Warning notifications for each pollutant source according to measurement items.