sensors Article SensoTube: A Scalable Hardware Design Architecture for Wireless Sensors and Actuators Networks Nodes in the Agricultural Domain Dimitrios Piromalis 1,2,* and Konstantinos Arvanitis 1 1 Department of Natural Resources Management and Agricultural Engineering, Agricultural University of Athens, Iera Odoos 75, Athens 11855, Greece; [email protected] 2 Department of Automation Engineering, Piraeus University of Applied Sciences (TEI of Piraeus), P. Ralli and Thivon 250, Egaleo 12244, Greece * Correspondence: [email protected]; Tel.: +30-697-232-9223 Academic Editor: Kemal Akkaya Received: 14 April 2016; Accepted: 29 July 2016; Published: 4 August 2016 Abstract: Wireless Sensor and Actuators Networks (WSANs) constitute one of the most challenging technologies with tremendous socio-economic impact for the next decade. Functionally and energy optimized hardware systems and development tools maybe is the most critical facet of this technology for the achievement of such prospects. Especially, in the area of agriculture, where the hostile operating environment comes to add to the general technological and technical issues, reliable and robust WSAN systems are mandatory. This paper focuses on the hardware design architectures of the WSANs for real-world agricultural applications. It presents the available alternatives in hardware design and identifies their difficulties and problems for real-life implementations. The paper introduces SensoTube, a new WSAN hardware architecture, which is proposed as a solution to the various existing design constraints of WSANs. The establishment of the proposed architecture is based, firstly on an abstraction approach in the functional requirements context, and secondly, on the standardization of the subsystems connectivity, in order to allow for an open, expandable, flexible, reconfigurable, energy optimized, reliable and robust hardware system. The SensoTube implementation reference model together with its encapsulation design and installation are analyzed and presented in details. Furthermore, as a proof of concept, certain use cases have been studied in order to demonstrate the benefits of migrating existing designs based on the available open-source hardware platforms to SensoTube architecture. Keywords: wireless; sensors; actuators; networks; open-source; expandable platforms; Arduino; ARM; energy management; agriculture 1. Introduction Wireless Sensors and Actuators Networks (WSANs) is an established and challenging technology, with a great potential impact on the measurement, communication and control applications to a variety of activities of the modern postindustrial society. According to market analyses, WSAN node sales will constitute a multi-trillion market in the next few years [1,2]. Given the fact, during the last 25 years, the agricultural production sector has been transformed from a traditional labor-intensive sector into a technology-intensive one, it has been strongly considered as a very prosperous potential area for WSAN technology use. Indeed, a vast range of existing and future WSAN applications in agriculture have been identified and reported by many researchers [3–5]. Moreover, relatively-new terms have been introduced in current terminology, in order to express the trends in modern agriculture, such as: precision agriculture; precision farming; variable-rate management; etc. On the other hand, Sensors 2016, 16, 1227; doi:10.3390/s16081227 www.mdpi.com/journal/sensors Sensors 2016, 16, 1227 2 of 59 the majority of WSAN deployments in agriculture are taking place on a short-scale research and development basis, rather than on a large-scale commercial solutions basis. The massive expansion of WSAN technology in agriculture appears to lag behind the market’s expectations. Many researchers haveSensors reported 2016, 16 certain, 1227 technological causes for this, which relate to hardware design issues,2 of 59 such as standardization in protocols and development tools, configurability, expandability, scalability in computingplace on power, a short-scale and memory research capacity and development [3,6–9]. basis, rather than on a large-scale commercial solutions basis. The massive expansion of WSAN technology in agriculture appears to lag behind the Examining the idiosyncrasy of the real-world (real-life) WSAN applications, the most common market’s expectations. Many researchers have reported certain technological causes for this, which criticalrelate features to hardware found are:design the issues, operation such inas thestandardization real environmental in protocols and and spatiotemporal development conditionstools, (far awayconfigurability, from the expandability, lab), the systems scalability are on in the computing end-users power, hands, and thememory energy capacity autonomy, [3,6–9]. the need for long-termExamining serviceability the idiosyncrasy and management, of the real-world the maintainability, (real-life) WSAN the expandability, applications, the the most reconfigurability, common the reusability,critical features the robustness found are: the and operation ruggedness, in the the real long-standing environmental reliability and spatiotemporal and the low conditions cost per (far WSAN nodeaway [10]. from Therefore, the lab), any the single systems factor, are on which the end-us can negativelyers hands, the affect energy one autonomy, or more of the the need aforementioned for long- features,term couldserviceability jeopardize and management, the success the of themaintainabilit whole WSANy, the expandability, implementation. the reconfigurability, Regarding agriculture, the thesereusability, features have the robustness greater impact and ruggedness, to the success the long-standing of WSAN applications, reliability and because,the low cost traditionally, per WSAN this sectornode requires [10]. Therefore, scalable wireless any single networks factor, which comprised can negatively by large affect number one or of more nodes of the covering aforementioned huge physical features, could jeopardize the success of the whole WSAN implementation. Regarding agriculture, remote areas, capable of measuring a variety of physical parameters [11]. Furthermore, very often, the these features have greater impact to the success of WSAN applications, because, traditionally, this harshsector operating requires environment scalable wireless has been networks reported, comp byrised many by experts, large number as a major of sourcenodes covering of implementation huge problemsphysical [12 remote,13]. Extreme areas, capable temperatures, of measuring humidity, a variety rain, of physical snow, wind,parameters and [11]. sunlight Furthermore, radiation, very can all seriouslyoften, threatthe harsh the operating normal operationenvironment of has WSAN been hardwarereported, by systems, many experts, which, as ina major their vastsource majority, of haveimplementation been designed problems for indoor [12,13]. environments Extreme temper (labs,atures, offices, humidity, etc.) rain, [6,9 snow,,14–16 wind,]. Unfortunately, and sunlight the physicalradiation, agricultural can all seriously environment threat cannot the normal successfully operation be of modeledWSAN hardware and tested systems, by simulation which, in their methods (e.g.,vast [17]). majority, For example, have thebeen behavior designed of for real indoor batteries environments [18,19] or the (labs, radio offices, signal etc.) propagation [6,9,14–16]. [20 ,21] are typicalUnfortunately, cases of the operation physical parametersagricultural environm that are extremelyent cannot successfully difficult to modelbe modeled and and fully tested simulate, by so the designsimulation of hardware methods WSAN(e.g., [17]). systems For example, for the the agricultural behavior of domain real batteries is more [18,19] complicated or the radio than signal in other propagation [20,21] are typical cases of operation parameters that are extremely difficult to model application domains. and fully simulate, so the design of hardware WSAN systems for the agricultural domain is more Sincecomplicated the early than days in other of the application WSAN technology domains. up to today, nodes’ hardware architecture was solely governedSince according the early to days the block of the diagramWSAN technology depicted up in Figureto today,1[ nodes’22,23]. hardware It is a microcontroller-based architecture was systemsolely with governed all the necessaryaccording to circuitry the block for diagram sensors, depicted and actuators, in Figure 1 equipped [22,23]. It is with a microcontroller- a radio frequency transceiverbased system for data with communicationall the necessary andcircuitry networking. for sensors, and Even actuators, recent researchequipped attemptswith a radio to use field-programmablefrequency transceiver gate for arrays data communication (FPGAs), instead and ofne microcontrollertworking. Even recent units research (MCUs), attempts in WSAN to use nodes are basedfield-programmable to the traditional gate architecture arrays (FPGAs), [24, 25instead]. In general,of microcontroller such a node units can (MCUs), be appropriately in WSAN nodes software configuredare based to to operate the traditional either architecture as end-device, [24,25]. router, In general, coordinator, such a node or, can with be someappropriately extra modifications, software as coordinatorconfigured to with operate gateway either as functionality. end-device, router, The rolecoordinator, configuration or, with issome dictated extra modifications, by the networking