## 2 State of the Art  
Data Acquisition System (DAS) for the measurement of physical entities are very common and successfully used in many fields [1, 2, 3, 4, 5, 6, 7, 8]. Their use is also growing in some less conventional areas [9, 10, 11, 12] and they are seeing more and more applications in the preservation of cultural heritage [13, 14], principally in the environmental control of museum rooms. On the contrary, due to the lack of reliability [15], the lack of specific devices that allow overcoming the communication network access problems typical of remote sites, the absence of devices that meet the real control researchers' needs and the reduced energy autonomy in absence of electrical network, DAS are rarely used for preservation of cultural heritage applications placed in remote sites. Scientific progress leads to a constant and continuous improvement/renovation that allows overcoming the existing limits [16]. Withthis aim, many efforts have been made by researchers to explore satisfying solutions, e.g., some studies are addressed to the realization of specific multi-tier architecture, which decouples the measurement of data from both their memorization and presentation to the final users [17]. Usually, these researches use Wireless Sensor Networks (WSNs) as the first level of the architecture. In fact, WSNs provide autonomous and reliable operations, which reduce the overall costs for structural health monitoring to just a few percentage of those of a conventional cabled monitoring system [15]. Data locally stored are then sent to a remote server using a gateway connected to the Internet where, simply using a browser, the end users can access the information. Among these researches, an interesting artistic in-field application for building preservation is presented in [18], where \"SMARTBRICKS\" are used as platform to connect sensors to the local gateway; in [19] a WSN transmits the data using the Bluetooth technology; in [20] 2.400-2.483 GHz transmitters designed for their special button sensors are used, while in [17,21,22] ZigBee tx/rx devices are used. Other works aim to improve the already optimal performances of the WSNs, e.g., in [23] a new approach to maximize power saving of the singular nodes is developed, while in [24], the use of solar energy to supply the sensors is investigated. Other interesting works are instead focused on the software management of the WSN [25,26].  
All these studies have been developed for environments considered non-hostile, where electrical energy and telecommunication facilities are available, in fact they usually use a personal computer as local gateway and, to send local data, they use the Global System for Mobile (GSM) communication protocol as telecommunication infrastructure.  
Although partially inspired by the cited works, our system was created to be used in hostile scenarios, without any available communication facility and without power availability, incorporating a power supply coming from alternative energy sources (such as solar energy) and the ability to transfer data through all the possible communication technologies available on the market, such as GPRS, WiMAX and satellite connections.  
The system has the very significant benefit of using standard technologies, such as ARDUINO and ZigBee, allowing high reproducibility and, at the same time, it uses innovative technologies like the Raspberry, which reduces the costs compared to a traditional Personal Computer system. The flexibility of these technologies enables a high scalability of the number and type of sensors that can be used simultaneously. The use of an efficient device like the Raspberry grants the ability to take high quality pictures of the monitored work of art and to make them available to researchers. At the same time, the logic managing the system is innovative because, in order to extend the operational time of the entire system, it is aimed at the minimization of energy consumption.