## 4 Materials and Methods  
Taking into account, not only the necessity to keep a healthful and productive workplace for the students, teachers and the school staff, but also to provide a consistent and regulated state of control for laboratory activities, the _iAQ+_ solution has been created by the authors. The _iAQ+_ solution provides a low-cost and reliable method for IAQ supervision which incorporates easy configuration and easy installation features. This system is a low-cost, reliable system that can be easily configured and installed by the average user without supporting the cost of an installation done by certified professionals. The main objective is to provide proper supervision of the LEC, such as air temperature, humidity and barometric pressure and a qualitative air quality index. Therefore, the authors selected a cost-effective BOSCH BME680 sensor, a four-in-one multi-functional microelectromechanical system (MEMS) environmental sensor which integrates a Volatile Organic Compounds (VOC) sensor, temperature sensor, humidity sensor and barometer. The DFRobot Gravity BME680 environmental sensor was used as it provides a Gravity I2C connector, is plug & play and is easy to connect. The _iAQ+_ is based on a microcontroller with built-in Wi-Fi compatibility, a FireBeetle ESP8266 (_DFRobot_). Figure 2 presents the hardware prototype developed by the authors. In this section, the hardware and software development materials and methods will be discussed. A brief introduction of each component used is shown below. * **FireBeetle ESP8266** is 32-bit Tensilica L106 microcontroller module which supports IEEE802.11 b/g/n WiFi (2.4 GHz-2.5 GHz). This module support one 10-bit analogue input, 10 digital inputs which incorporate multiple interfaces such as SPI, I2C, IR, and I2S. The clock speed is 80 MHz and can reach a maximum 160 MHz; in addition, it includes a 50 KB SRAM and 16 MB flash memory. It supports a low-power-consumption mode of 46 uA and the operating voltage is 3.3 V.
* **DFRobot Gravity BME680** is an I2C environmental VOC sensor, temperature sensor, humidity sensor and barometer. It supports an input voltage of 3.3-5.0 V; the operating current consumption is 5 mA without air quality sensing and 25 mA with air quality features. This sensor module size is 30 \(\times\) 22 mm / 1.18 \(\times\) 0.87 inches. The temperature range is from -40 \({}^{\circ}\)C to +85 \({}^{\circ}\)C with a precision of \(\pm\)1.0 \({}^{\circ}\)C (0-65 \({}^{\circ}\)C). The humidity range is from 0 to 100% r.H with a precision of a \(\pm\)3% r.H. (20-80% r.H., 25 \({}^{\circ}\)C). The atmospheric pressure measurement range is from 300 to 1100 hPa with a precision of \(\pm\)0.6 hPa (300-1100 hPa, 0-65 \({}^{\circ}\)C). * **DFRobot Buzzer Module** is a buzzer module that supports an input voltage of 3.3-5.0 V.  
Figure 2: _iAQ+_ prototype. * **5V Green LED**--a 5 V green LED is used to notify the end-user of a good IEQ conditions. * **5V Red LED**--a 5 V red LED is used to notify the end-user of poor IEQ conditions. The BME680 sensor calculates the sum of VOCs in the surrounding air to provide qualitative air quality data. This sensor incorporates a background auto-calibration feature in order to provide reliable IAQ qualitative data. This process regards the recent measurement records to guarantee that IAQ index \(-\)25 matches to typical good air and IAQ index \(\sim\)250 states for typical polluted air. The sensor output resistance value varies according to VOCs concentrations, the higher the concentration of reducing VOCs, the lower the resistance and vice versa. The IAQ qualitative range is from 0 to 500 (the larger, the worse). Table 2 illustrates the IAQ qualitative index meaning of the selected sensor. The mobile application, designated as _iAQ+Mobile_, was created using SWIFT programming language in XCode IDE (Integrated Development Environment), and the minimum requirement is the iOS 12.