In the last year the objectives for the students were to create two different units that measure air temperature, relative humidity, air pressure, atmospheric pollution and UV index. Both of them transmit the measured data to a central unit to analyse them. One of these units has been fixed on the ground (outside of the physics lab's window, in a protected area, Fig. 4b) and the other do measurements during flight on a certain height (like a CanSat). The mobile unit is easy to assemble during a classroom activity and to connect with a radio-transceiver module (built before). The idea of a flying device was born after one of the “CanSat in Europe” competition held by ESA (European Space Agency), where the Science Club team took part. (For details of such a competition see the ESA CanSat webpage at https://www.esa.int/Education/CanSat/What_is_a_CanSat, ESA CanSat, 2019.) The students have utilized the experience gained in this contest to build a quadcopter lifted measuring unit. A very small and light device (fit in a coca-soda can) with pressure, temperature, relative humidity, air quality sensors with GPS and altimeter was made to fulfil the task. Both units (the fixed and the flying) are Arduino microcontroller based measuring instruments, which were designed, built and operated by students (Pető, 2014; Pető, 2017a, c). The used Arduino Uno or Redboard (Fig. 1) are open-source electronics platforms with an Atmega328 chip, easy to connect with a large variety of electronic sensors (Margolis, 2011).

The first step in the project is a brainstorming session when the best-fitting device is chosen, the measuring methods and the outcome are also found out. At the beginning stage, the pupils use their creativity to discover the best possible solution to the problem. Meanwhile, they acquire basic knowledge about electrical circuits, measuring principles, Arduino microcontrollers, sensors (e.g. Fig. 2), data collecting and analyzing procedures, programming languages and atmospheric physics.

This is an intense learning phase, where the theoretical knowledge (electric power, current intensity, resistance, Ohm's law, etc.) is applied in a concrete practical situation. Simple circuits are designed and built by the students using few elements: power supply units, a variety of resistor networks, active and passive circuit elements, switches and measuring instruments with suitable accuracy. The result of this process is that the learned theories are fixed and, in the meantime, the students are enriched with practical knowledge (Pető, 2016).

Another challenge becomes obvious while designing the circuit (Fig. 3). For the measuring units, a circuit design and a printed circuit board have to be made. Students should consider what kinds of sensors are the most appropriates (based on their electrical characteristics and datasheet) and how to connect them to make an effective measurement. By selecting sensors and power supplies, the planning work will be completed.

The next step is to draw the circuits and to carry out a testing measurement on a breadboard. Based on the results obtained, the circuit structure could be improved, some sensors can be replaced or extended. Meanwhile, attention should be paid to economical use of space, all circuit elements have to function on the planned parameters (in a relatively small place), and these have to be easy controllable.

The younger students use the Fritzing software to design the circuit, learned from their mentors. In the course of the the design process, they will learn the measurement principles of the sensors, the communication protocols and the connection types of the circuit modules. Once the designing and the block diagram for the operating system is completed, one part of the team should prepare the printed circuit boards (PCB) and the sensors for soldering. The teams prepare more than one test unit for learning so they could practice the assembly phases and understand the operating principle. Simultaneously, the other part of the group starts to prepare the proper software (Margolis, 2011; Pető, 2017b, c).

The Arduino library and Arduino IDE are used to write the appropriate software to command the measuring sensors completed by the C++ language learned at IT classes. This creative process is another good opportunity for the student to use the acquired knowledge of computer science classes for a specific practical task.

Data processing and interpretation are very significant elements in understanding the physical background and cause-effect relationships behind the phenomena like the vertical temperature gradient law in the atmosphere, the barometric formula for the pressure, solid pollution distribution in the air, and the relationship between relative humidity and precipitations.

Another considerable step in data processing is the graphic representation, interpretation and tracking the data over a long period. As a result, the formulated conclusions and answers are much accurate and could be verified, combined with knowledge learned at biology, chemistry or geography classes (Ahrens and Henson, 2016; Marshall and Plumb, 2008; Wallace and Hobbs, 2006).

We often do measurements on hillside near the city with a mobile device. Similar sensors are built into this unit, complemented by a GPS and a radio transmitter. The flying unit is lifted of distinct heights with a quadcopter. The unit send data to a central ground unit using a 433MHz RF transceiver system (this unit is built at Science Club in advance), measured at a few hundred meters altitude, and the fixed one use a wireless transmitting module. The data recorded by the ground (Fig. 5) and flying modules (Fig. 6) are collected in a dedicated computer database and then are analysed and compared during special activities (Pető, 2014).