## 1 Introduction
A practical respond to overcome the know-how shortages, was the adoption of ready-made hardware solutions available in the market and their integration, in order to build final applications. This is commonly referred to as the commercial-of-the-shelf (COTS) approach. COTS are met either in the form of ready-made WSAN nodes, also known as motes, designed according to the traditional architecture [43], or in the form of specific-oriented testbeds. Admittedly, COTS-based systems design is an attractive approach for many practical reasons: it helps to reduce the development time, it absolves developers from re-inventing the wheel, it closes knowledge and skills gaps by providing ready-made resources (protocol stacks, etc. ), it is relatively lower in cost compared to new prototype systems that suffer from high non-recurring engineering (NRE) costs [44; 45; 46; 47]. However, the adoption of COTS approach precludes, in many cases, the deliberation of researchers and practitioners to extend their study and application areas. Furthermore, COTS-based solutions have not been designed in order to cope with the harsh external environmental conditions of specific applications, as in the case of agriculture. Therefore, this hardware design approach appears to be one-way, for building pilot and proof of concept units, but due to the limited expandability and reconfigurability imposed by various bounded architectures (in fact, slightly modified alternatives of the traditional architecture of Figure 1), it is incapable of supporting the requirements of real-world WSAN applications, especially in the agricultural domain [9; 28; 41; 48]. WSANs' developers in their persistent search of hardware platforms that allow for reconfigurability and expandability, have often recurred to generic open-source hardware (OSH, or OSHW) solutions such as the Arduino, Raspberry Pi and others [49; 50; 51]. Such platforms have been mainly created for embedded systems students and hobbyists. In particular, all of these solutions rely on the scenario of a MCU-based board that can be programmed using easy-to-learn C-language functions (through application peripheral interface (API) libraries) and are easily expanded using pass-through pin-headers by connecting additional application-specific boards. A huge number of ready-made firmware applications, examples and other programming resources have been produced and are freely available as open-source code from an extremely big developers' community. This is very attractive for engineers and researchers who wish to overcome the limitations of embedded systems design and programming [3; 41; 52]. In agriculture there are already WSAN applications, where the aforementioned multi-board platforms have been used, either in cases of new system designa, or in cases of modifications to expand the functions of existing systems [9; 14; 49; 53]. Summarizing, all the existing hardware design approaches, namely, the traditional architecture, the COTS-based approach, and the expandable OSH multi-boards platforms, appear to impose significant limitations and they inhibit the expansion of real-world WSAN implementations. Under these circumstances, the end-users in agriculture are very skeptical regarding the benefits-to-cost ratio. Robust and reliable WSAN systems tolerant of real-world applications needs, is a mandatory factor for WSAN credibility [8]. As it has been highlighted in [3], there is a lack of complete frameworks capable of allowing the development of systems from data acquisition to modeling and decision support. Therefore, it is obvious that the required new platforms should meet both the research needs and the needs entailed by real-life applications in the field of agriculture. This paper proposes the SensoTube, as a new open-source-oriented architecture for designing WSAN systems, with emphasis on the real-world implementations in the agricultural domain.