# Noise Impact Analysis of School Environments Based on the Deployment of IoT Sensor Nodes
## 2 Methods
### Station Design: IoT Sensor Nodes  
The Wi-Fi-based IoT sensor nodes comprise a WeMos D1 R2 development board [24], which incorporates an ESP-8266 microprocessor and a Wi-Fi card. On the other hand, as mentioned in the previous sections, in the case of data collection and data transmission and reception from the senior high school building to the building of the high school, a Wi-Fi LoRa 32 (V3) device from the Heltec Automation [25] development board was utilized. It includes an ESP32-S3 FN8 microprocessor and both a Wi-Fi and a LoRa wireless card. Regarding the acoustic signal level sensor, we finally used the SEN0232 analog sound level meter as discussed in Section 2.2[22]. The temperature and relative humidity measurements were conducted by employing the DHT11 [26] and AHT10 [27] sensors. The DHT11 sensor is a digital sensor that supports a relative humidity measurement range of 20-90% with \(\pm\)5% accuracy, a temperature measurement range of 0-50 \({}^{\circ}\)C with \(\pm\)2 \({}^{\circ}\)C accuracy, and a maximum current consumption of 2.5 mA. It features 3 pins (VCC, ground, and digital output). The digital output that provides the measurement data to any of the digital I/O pins of the used board. On the other hand, the AHT10 sensor provides 4 pins (VCC, ground, SDA, and SDCL). The AHT10 sensor uses the I2C (0x38) interface to feed its measurements to the board of the IoT sensor nodes by connecting the data pin SDA to the D2 pin (RX) of the boards while connecting the SCL pin to the D1 pin (TX). The AH10 sensor specification facilitates a temperature measurement range of \(-\)40 \({}^{\circ}\)C to 85 \({}^{\circ}\)C (\(\pm\)0.3 \({}^{\circ}\)C accuracy) and a relative humidity measurement range of 0% to 100% (\(\pm\)2%RH  
Figure 5: (**a**) The location of Station 21 in the 2 nd building within the red cycle; (**b**) the location of Station 10 and LoRa Rx in the 1 st building; (**c**) Station 10 and LoRa Rx.  
accuracy). Both sensors are low-cost and adequate to efficiently support the monitoring of the environmental settings in school buildings because they have been deployed inside them and are not affected or exposed to severe weather conditions like rainfalls or direct sunlight, something that would deteriorate their operation. As mentioned in previous sections, three types of data collection stations were designed and implemented, as shown in Figure 6. Table 1 summarizes the equipment used in the 3 different IoT sensor nodes.  
Figures 7 and 8 delineate, respectively, the operation flow of the Wi-Fi-based IoT sensor node and the LoRa-based IoT one. Specifically, the Wi-Fi-based station acquires the environmental temperature and humidity measurements every 20 min and the sound level every 5 min. The data are sent to the MQTT broker via the Wi-Fi connection. If the measured noise level is above 85 dBA (presence of high noise levels according to WHO standards), the sampling period is increased to every 1 s to record the noise behavior  
\begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{1}{c}{**Equipment**} \\ \hline
**Type** & **Device** \\ \hline Acoustic Signal Sensor & SEN0232 \\ LoRaWAN and Wi-Fi Board with & \\ ESP32-53 FN83 microprocessor & Wi-Fi LoRa 32 (V3) Heltec \\ Wi-Fi Board with ESP-8266 microprocessor & WeMos D1 R2 \\ Temperature and Humidity Sensor & DHT11 \\ Temperature and Humidity Sensor & AHT0 \\ \hline \hline \end{tabular}
\end{table}
Table 1: IoT sensor node equipment summary.  
Figure 6: (**a**) The Wi-Fi-based IoT station comprising the DHT11 and the SEN0232 sensors; (**b**) the Wi-Fi-based IoT station comprising the AHT10 and the SEN0232 sensors; (**c**) the LoRa-based IoT station comprising the DHT11 and the SEN0232 sensors.  
in detail. On the other hand, for simplicity reasons, due to the LoRa transmission, the LoRa-based station reads the temperature, humidity, and noise level values every 3 s.