The electronic system used for data collection consists of the following components:

• UNO R3 development board with Arduino compatible ESP 8266 WiFi module
• External battery pack POWERZILLA PZ 11000, 11000 mAh.
• Breadboard MB102 + 3.3V and 5V Power Source
• Sensors
• MQ-4 Gas sensor - used for detecting natural gas and methane
• MQ-9 Gas sensor - used for detecting carbon monoxide
• MQ-135 Air Quality sensor - used for determining air quality
• Optical particle GP2Y1014AU0F sensor - used to determine the concentration of dust particles in the atmosphere on the basis of which the parameter of interest PM2.5 was established
• Connecting wires
• Dupont wires - used to connect the development board and sensors
• USB-A to micro USB-B cable male/male - used to power the development board from the external battery
• USB-A to USB-A cable male/male - used to power the breadboard from the external battery
• LCD1602 screen - electronic display with two lines of 16 characters each
• I2C LCD 1602 interface module - the module used to reduce the number of pins on the development board which are needed to be connected to the LCD1602 screen. This way it only occupies the A4 and A5 pins corresponding to the SDA and SCL signals in the I2C transfer protocol respectively.

The UNO R3 compatible module is programmed to wait periodically to receive a Request command from the ESP module. Once the command is received, the module reads the data transmitted in serial format by the connected sensors, and sends them a Response command in JSON format to the ESP module.

The ESP8266 module is programmed to connect to a Wi-Fi network at startup, and then to connect to the MQTT broker: broker.mqtt-dashboard.com.

After the initial connections, the module will periodically send Request messages to the UNO R3 module, in order to receive from it the data taken by the sensors. The received data are then published in a predetermined MQTT topic, from which they will be taken later by another component of the IoT system.

The purpose of this work for later use is in a geographically distributed network of sensors, and a possible implementation is for the network to be made up of a number of drones, each equipped with a measuring system.

Therefore it was considered necessary to provide a method of encapsulating the system in a hermetically and thermally insulated enclosure. However, airtight and thermal insulation is also indicated in the usual use of the system, primarily due to the fact that the system contains fragile components, which makes it vulnerable to shocks. and the electrical nature of the structure makes it susceptible to atmospheric phenomena or even human accidents. Second, it is desirable that the measurements made by the system be as accurate as possible, despite the impossibility of ensuring laboratory conditions in which all components can be calibrated and operate at optimum parameters. Each component that makes up the system, and especially the sensors, offers different performance depending on the ambient temperature, in the case of sensors, the laws of measurement differ drastically.

Thus, the encapsulation of the system ensures a controlled environment of the measure, reducing as much as possible the disturbed and external effects. 4 liters. The dimensions of the box are 31x19x12, being represented in centimeters. The box is resistant to a range of temperatures between 25 ° C and 95 ° C, sufficient temperatures to ensure the safety of the system in the environment to be measured.

A public MQTT broker is used to retrieve the data collected by the electronic data collection system: broker.mqtt-dashboard.com. In it I published the ESP8266 module messages in the test/Sabin topic, using the test/Sabin/Sensor_Data and the test/Sabin/Configuration subtopics.

The data transfer mechanism is built in the Python programming language and consists of two main components.

The first component is a subscriber to the whole test/Sabin topic so it will receive messages from any of its subtopics. When a message in the test/Sabin/Configuration subtopic is received, this will update the variable containing the calibration time. This calibration time is necessary because the development board transmits the start-up time, which is added to the calibration time to obtain the exact time at which the measurements were executed. When a message in the test/Sabin/Sensor_Data subtopic is received, it will transmit the data to the second software component.

The second software component is a mechanism for processing data, building and sending SQL commands. Based on the data read by the sensors, received from the MQTT subscriber, the component extracts the measured concentrations following the methodology. It then builds SQL commands to insert this information into the MySQL database.

The entire flow is:

In this paper, a Web application was created for visualizing data, starting from an open source template that provides examples of creating different graphical interface elements within the application. The table elements were created using the DataTables software opensource licensed under the MIT license, and graphics were created using the Chart.js software as well as the open source MIT license.

The web application is designed to be used by three types of users, for whom different types of applications have been created.

• Typical user - The type of user who can view the air quality information processed and receive statistics and announcements. A user can also access theoretical information on air quality and measurement methodology used in the project and, if necessary, can submit requests for technical assistance.
• Observer - The type of user who can access the data taken by the sensor in raw information, also receives statistics and announcements, and can publish in turn or an announcement. In addition, the observer can access information of a theoretical nature. Depending on the air quality and the measurement methodology used in the project, it may, if necessary, submit requests for technical assistance.
• Administrator - A type of user whose purpose is to administer the created platform, who can view information about regular users and observers. you need to fix them and add or delete users.

In the following, several snapshots from the application will be listed:

Login Page:

Register Page:

Administrator Dashboard:

Application user view:

User Dashboard:

User data graph visualization:

User statistics visualization:

User assistance request form:

The technical specifications of the built measurement set are:

• Measurement system weight - 460g
• Measurement system box weight - 452g
• Total weight - 912g
• Dimensions - 33.5cm x 23cm x 16cm
• Autonomy - approx. 21 hours
• Realization cost - approx. 250RON
• Necessities - In addition to pre-charging the external battery, only WiFi connection is required.

== Prospects for improvement and further development =

lthough the performance of the realized system is very good, and the parameters of interest have been mainly fulfilled and successfully, there are improvements, which can or could be improved, and even more the quality of this system. .