## 5 Electronics
In order to control them, it is necessary to include a microcontroller. In this case, Arduino Nano has been chosen because, presenting enough computational capacity, it has a very low energy consumption. Moreover, since all these components require a constant voltage of 5 V, which is higher than the battery's one, a boost converter is required. This paper has installed a SparkFun PRT 10255 Boost Converter [54]. The monitoring system is in turn composed of two different parts. On the one hand, active sensing of six temperatures and four power generations is performed, thus simulating the existence of sensors in a real station while monitoring the operating conditions of the prototype. These measurements are taken every 4 min thanks to Maxim Integrated MAX31855 PMB1 peripheral modules (with type K thermocouples) and Adafruit INA219 breakout boards respectively [55; 56]. In order to avoid errors, these measurements are repeated 15 times, and the average of all the valid ones is stored. On the other hand, there is an extra consumption simulated passively with electrical resistors that includes peaks of demand, which are typical in vigilance stations. Hence, there is a constant power requirement of 0.3 W and every 12 min, a peak of consumption of 0.5 W occurs during 2 min. For this purpose, one of the outputs of the Arduino is connected to a MOSFET, so that an electrical resistor is directly connected to the battery when determined by the microcontroller. All the data registered by the active sensors needs to be emitted to a reception center. Nevertheless, this process usually requires a high energy consumption [18]. Therefore, the present paper investigates low energy communication systems that, while being able to communicate wirelessly over a considerable distance, facilitate thermoelectric generation as the power supplier. Low-Power Wide-Area Network (LPWAN) standards, typically associated with Internet of Things (IoT), meet these requirements. Hence, this work analyzes the five technologies that seem to have the widest market potential: SigFox, LoRaWAN (Long Range WAN), IEEE 802.15 promoted by Wi-SUN (Wireless Smart Ubiquitous Network), and 3 GPP standards: LTE-M (LTE for M2M) and NB-IoT (Narrow Band IoT) [57]. Figure 6: Diagram of the electronics installed with the prototype, which represents the node of the LoRa communication system. Table 2 summarizes the main characteristics of the former technologies in relation to their frequency band, maximum data rate, range (or coverage) and power usage [58; 59; 60; 61; 62; 63]. As can be observed, within the table two categories can be distinguished. On the one hand, there is a category composed of LTE-M and NB-IoT, which use the current cellular telecommunications bands, since they are indeed extensions of the 4G network infrastructure. As a consequence, their range is extensive, but present a medium power usage, leading to their discard for the application under consideration in this paper. On the other hand, SigFox, LoRaWAN, and Wi-SUN use the unlicensed ISM frequency bands and present low power usage. SigFox was one of the pioneers in the LPWAN market and it targets the very low power and low bandwidth applications, while offering very good coverage characteristics. Nevertheless, it is not available everywhere and it requires the payment of a royalty. On its behalf, LoRa is completely open and permits faster data rates, although the coverage range is curbed. Finally, Wi-SUN is focused on applications within public utilities, smart homes and smart cities, and therefore presents a reduced range of 5 km. The present paper represents the first approximation for an autonomous volcanic monitoring station. Hence, the remoteness of volcanoes leads to the discard of Wi-SUN. Among SigFox and LoRa, the latter is preferred because, although it has a smaller coverage, it permits a higher data rate, it is completely free and it can be implemented everywhere. Due to these advantages, LoRa was also the technology chosen by [PERSON] et al. and [PERSON] et al.