# A Social Environmental Sensor Network Integrated within a Web GIS Platform
## 3 Implementation
### Hardware  
The system developed within this study may be seen as an extension of a wireless sensor network and consists of several hardware parts. The system aims at monitoring the immediate conditions related to the perceived environment. Its hardware components consisted by a control unit and several sensors able to record and disseminate the ambient conditions of a given area. The components need to comply with the conditions of replace-ability, availability and programmability in order to facilitate ease of operation and reproduction. Electronic prototyping offer several off the shelf solutions that follow the aforementioned criteria. The sensing device is developed using an Arduino developing board. More specifically, we opted for the Arduino YUN [29] which may be easily deployed for both portable and fixed operation due to its networking capabilities and expand-ability. Arduino platform offers low power consumption among popular open source development boards. Additionally, Arduino offers distinctive Digital and Analogue pins, enabling connectivity with several sensors, actuators and modules. The YUN model offers extensive wired and wireless connectivity capabilities along with Arduino's Integrated Development Environment (IDE). The latter is based on C and C++ languages, which loads cyclic programming loops directly through the device's firmware. Physical quantities of specific environmental variables are produced by 5 sensor modules that have been connected on the YUN (Table 1). In addition to monitoring tasks the YUN operates as a communication node that transmits the measurements through WiFi (while being fixed) and Bluetooth (while being mobile). The selected sensor modules have been selected based on low cost and their range of calibration, taking into consideration as many variables as possible. The schematic of the sensor node, built using an Arduino YUN is illustrated in (Figure 1). The selected components are depicted in Table 1 and they have been selected based on their low price and adequate accuracy for the proposed application, i.e., accuracy was sufficient for the goal of qualitative assessment of environmental parameters. We should note that the necessary source code for the sensor node and the mobile phone has been made publicly available (Mobile Sensor: [[https://goo.gl/oKqw5a](https://goo.gl/oKqw5a)]([https://goo.gl/oKqw5a](https://goo.gl/oKqw5a)), Fixed Sensor: [[https://goo.gl/9](https://goo.gl/9) RJvRU]([https://goo.gl/9](https://goo.gl/9) RJvRU), Android App: [[https://goo.gl/BuPUoh](https://goo.gl/BuPUoh)]([https://goo.gl/BuPUoh](https://goo.gl/BuPUoh)). When being fixed, the system is directly connected to WiFi, while being portable, An Android device (i.e., a typical smart-phone) complements the system's hardware in order to provide connection to the Internet. More specifically, the smart-phone acts as a base station that receives and transmits flow of data from the sensors to the server. Furthermore it may also offer extensive control and real-time visualization features for the purpose of complete monitoring operation. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Expansion Type** & **Model** & **Function** & **Measurement Unit** \\ \hline Temperature, Humidity & DHT 22 & Temperature, Rel. Humidity, Heat Index & \({}^{\circ}\)C, \% Humidity, \% \({}^{\circ}\)C \\ Photometer & TEMT 2000 & Luminosity & Lux (lx) \\ Microphone & MAX 4466 & Noise Pollution/ Noise Intensity & dBm \\ Gases microparticles & MQ-7 & Carbon Monoxide (CO) & ppm \\ Gases microparticles & MQ-4 & Methane (CH4) & ppm \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Expansions, Functions and Units used on the recording devices. The selection of the aforementioned hardware components attempts to tackle the common problem of insufficient energy resources, especially in mobile operation (Figure 2). The Arduino platform is known to offer several solutions for connecting to power sources, while having a relatively small energy footprint. In our case, the YUN is connected to a typical power bank via USB.