**6. Conclusions**

Development of digital electronic technologies enables design and application of embedded systems for different needs and applications. Such systems are maximally adapted to concrete application and are specialized and optimized for a specific purpose. Different hardware and software platforms can be used for design and implementation of such systems. Specially designed platforms are the most often used for such purposes. But, in many practical needs it is much more convenient to use open source hardware and software platforms.

It is proposed here to use open source hardware and software microcomputerbased technologies for design and implementation of embedded systems for many practical applications. As illustration of such approach and its benefits, two such practically designed and implemented embedded systems were presented and described. Open source microcomputer boards, appropriate sensors, actuators and additional electronics were used for the systems hardware implementation. Open source software tools and programs and LINUX operating system were used for the systems software implementation. Modular approach that enabled easy expandability, simplifying maintenance and adaptation of the system to user needs was also used in the system design. It was also achieved balance between functionality and cost of the systems.

It was performed optimization in selection of all used components and tools, and optimization of all hardware and software designs, according to system needs, in the design and implementation of this embedded systems. Such it is achieved balance of functionalities and cost of the system. Main advantages of this embedded systems compared with other ways of design and realization are: lower cost, optimization according to application, smaller dimensions and weight, and lower electrical energy consumption. Some disadvantages are: lower reliability, lower certainty, constrained application on need for what the system was designed.

The Arduino hardware platform was chosen for the systems realization because that platform is easy available, very good documented, with many development tools, very cheap and can satisfy all needs of the systems concrete application with the small system cost. It is especially case with the system for user identification using smartphone that is relatively simple system. The Linux operating system was used in implementation of SCADA and RFID system since that system is more complex and not requiring high speed of operation. So, LINUX operating system was chosen because it enables faster and simpler design of system software, shorter system development time and smaller cost of the system.

Embedded systems based on open source platforms are not standard general purpose solutions or totally specially designed solutions. Such systems are less expensive, specialized and optimized solutions for some concrete user need. Such design and implementation should be used mainly for systems of smaller or medium complexity and where is needed smaller number of the systems. That approach can also be used for design and implementation of more complex and larger embedded systems. But, then it will be needed much more activities and time for system design and implementation and systems will be more expensive.
