## 9 Discussion and Conclusions  
A new architecture for hardware design of WSAN systems was presented in this work. The aims of the SensoTube architecture, as defined in Section 3, have been rather successfully met. The existing end-solutions and COTS-based WSAN systems in their vast majority have been designed based on the traditional architecture (see Section 1, Figure 1), which basically places the emphasis entirely on the wireless networking aspects. This is reasonably explained by the fact that a decade ago the WSAN technology was very new and the efforts had to be diverted towards the design of hardware, which would primarily support the development, the evaluation and the demonstration of that revolutionary technology. Nowadays, when WSANs can be considered as a mature technology and the interest has shifted from the core technology to its embodiment in real-world applications, the rigidity of the traditional architecture appears to constitute a significant barrier for the expansion of WSAN solutions. The abstraction of the SensoTube architecture provides the necessary design framework with which the real needs of a WSAN system can be accommodated, so each functional aspect of the system can have a clear, predefined space, in order to be tidily implemented without, at the same time, conflicting with other functions of the system. In particular, the seven functional layers proposed are: the data acquisition and control layer (DCL), the wireless networking layer (WNL), the data gateway layer (DGL), the application-specific layer (ASL); the programming and debugging layer (PDL), the power management layer (PML), the evaluation and testing layer (ETL). Thus, the hardware designers, as well as the developers of different specializations, can know in advance how to jump into the WSANs field and at which particular function their design contribution belongs to. Hence, the proposedfunctional abstraction can support the integration of several challenging technologies that could potentially have a positive impact on the design of real-world application-oriented WSAN systems. Regarding the practical side of the hardware design, the seven SensoTube functional layers' ability to be realized in the form of discrete expansion shields ensures that the benefits of the popular open-source hardware platforms will be experienced by all those involved. However, it is totally meaningless to design any of the new functional shields just as another expansion shield for one of the existing expandable platforms, because, although these platforms are very convenient for small-scale prototyping and proof-of-concept implementations, in practice, they cannot be considered as a reliable solution for real-world WSAN applications, such in the case of agriculture (see Section 2). Also, an insurmountable obstacle in the adoption of the existing expandable OSH platforms is that they do not allow for real scalability and expandability, which actually is a key factor for the accommodation of a hardware abstraction, such as the one proposed by SensoTube. In accordance to the architecture of these platforms, the type and the number of the extension shields is determined by the features of the MCU of the main-board, so it is very common for designers to face resource limitations, such as in the processing power, the program memory size, the input/output signals, or the communication interfaces, and the only way to respond is to replace the main-board with one that has enhanced features, but jeopardizing in this way the compatibility with the already existed expansion shields. Moreover, practically none of the existing main-boards support the engagement of MCU-based shields, they do not care about how the expansion shields will fulfill their particular energy needs, and, they do not pay any attention on the form-factor of the expansion shields. Therefore, there are serious risks and troubles in WSAN systems based on these architectures.