# Development of Multi-Item Air Quality Monitoring System Based on Real-Time Data
## 2 Materials and Methods
### Hardware Process of Multi-Item Air Quality Monitoring System
\begin{table}
\begin{tabular}{c l} \hline \hline
**Sensors/Modules** & \multicolumn{2}{c}{**Characteristics**} \\ \hline \multirow{2}{*}{Particle Matter Sensor} & Method: light scattering method, Size 48 \(\times\) 41.5 \(\times\) 12.9 mm \\  & PM\({}_{10}\), PM\({}_{4.0}\), PM\({}_{2.5}\) and PM\({}_{1.0}\) \\  & Range 0–1000 \(\mu\)g/m\({}^{3}\), Accuracy \(\pm\) 10 \(\mu\)g/m\({}^{3}\) \\ \multirow{2}{*}{CO\({}_{2}\) Sensor} & Non-dispersive infrared absorption (NDIR) \\  & Size 35 \(\times\) 23 \(\times\) 7 mm \\  & Range 400–10,000 ppm, Accuracy \(\pm\) 30 ppm \(\pm\)3\% of reading \\ \multirow{2}{*}{CH\({}_{4}\) Sensor} & Non-dispersive infrared absorption (NDIR) \\  & Size 33 \(\times\) 33 \(\times\) 13.1 mm \\ \multirow{2}{*}{DS-CH\({}_{4}\)-D3} & Range 0–50,000 ppm, Accuracy \(\pm\) 3\% \\  & Electrochemical method, Size 2.5 \(\times\) 2.5 \(\times\) 0.9 mm \\ \multirow{2}{*}{Humidity Sensor} & \(-\)40 \(\lx@math@degree\)C to 125 \(\lx@math@degree\)C, with accuracy of \(\pm\)1 \(\lx@math@degree\)C \\ \multirow{2}{*}{(SHT30-DIS-B)} & 0\% to 100\%, with accuracy of \(\pm\)1\% \\  & UCCs Sensor & Electrochemical method, Size 2.45 \(\times\) 2.45 \(\times\) 0.9 mm \\ \multirow{2}{*}{(Sensirion\_SGP30)} & 0–60,000 ppb, Accuracy 15\% of meas. Value \\  & Electrochemical method, Size \(\Phi\)23.5 \(\times\) 24.5 mm \\ \multirow{2}{*}{O\({}_{2}\) Sensor} & 0–25\%, Accuracy \(\pm\) 0.1\% \\  & Electrochemical method, Size \(\Phi\)23.5 \(\times\) 24.5 mm \\ \multirow{2}{*}{H\({}_{2}\)S Sensor} & 0–100 ppm, Accuracy \(\pm\) 0.1 ppm \\  & Electrochemical method, Size \(\Phi\)23.5 \(\times\) 24.5 mm \\ \multirow{2}{*}{(Mixen\_NH\({}_{3}\))} & 0–100 ppm, Accuracy \(\pm\) 0.1 ppm \\  & Electrochemical method, Size \(\Phi\)23.5 \(\times\) 24.5 mm \\ \multirow{2}{*}{SO\({}_{2}\) Sensor} & 0–20 ppm, Accuracy \(\pm\) 0.1 ppm \\  & Electrochemical method, Size \(\Phi\)23.5 \(\times\) 24.5 mm \\ \multirow{2}{*}{NO\({}_{2}\) Sensor} & 0–20 ppm, Accuracy \(\pm\) 0.1 ppm \\  & Electrochemical method, Size \(\Phi\)23.5 \(\times\) 24.5 mm \\ \multirow{2}{*}{O\({}_{3}\) Sensor} & Electrochemical method, Size \(\Phi\)23.5 \(\times\) 24.5 mm \\ \multirow{2}{*}{(Mixen\_O\({}_{3}\))} & 0–20 ppm, Accuracy \(\pm\) 0.01 ppm \\ \multirow{2}{*}{CO Sensor} & Electrochemical method, Size \(\Phi\)23.5 \(\times\) 24.5 mm \\ \multirow{2}{*}{(Mixen\_CO)} & 0–1000\%, Accuracy \(\pm\) 1 ppm \\  & WiFi: \(\bullet\) 802.11 b/g/n\_IOT \\ \multirow{2}{*}{ESP8266 Serial WiFi} & Integrated low power 32-bit MCU, 10-bit ADC \\ \multirow{2}{*}{Module -ESP-12S} & \(\bullet\) Integrated TCP/IP protocol stack \\  & \(\bullet\) Integrated TR switch, LNA, power amplifier and matching network \\ \multirow{2}{*}{Bluetooth 4.2} & Frequency range: 2360–2483 MHZ \\  & Output power: 4 dBm \\ \multirow{2}{*}{NRF52832 Module} & Receiver sensitivity: –96 dBm Bluetooth \\ \multirow{2}{*}{NRF52832 Module} & Modulation method: GFSK \\  & Kernel: Cortex-M4F \\ \multirow{2}{*}{Module Size: 21 \(\times\) 25 mm Interface spacing 1.27 mm} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Sensors and Module characteristics in the multi-item air quality monitoring system. The methane sensor and carbon dioxide sensor were separately manufactured in the form of a probe rod so that they could be connected to the main device for measurement. A detailed picture is shown in Figure 3. The plastic used in the production was made of polycarbonate, which is a heat-resistant plastic. The measuring part is made of stainless steel and has a ventilation hole so that there is no problem in measurement, even in high heat. The biggest advantage of the developed measuring device is that it can measure many items at once, and the number of measurement items can be adjusted according to the user's needs through easy attachment and detachment of the sensor. Figure 2: Hardware of (**a**) multi-item air quality monitoring system device front part; (**b**) rear part.