## 5 Electronics  
The objective of the present paper is to develop an autonomous and robust volcanic monitoring station. Hence, since the generator part has already been analyzed, this section focuses on the electronic part associated to it prior to the installation of the whole system in a real volcano. These electronics, in order to resemble a real station, include a system to process the generated signal, as well as devices for acquiring data and emitting it wirelessly to a receptor. Their description will be based on the diagram shown in Figure 6, with the generation on the left side (with green arrows) and the consumption in the right one (with red ones). As can be observed, a prototype with four thermoelectric modules, this is two devices such as the one depicted in Figure 2, are considered to ensure a sufficient generation under real conditions, given that the heat transfer with the fumaroles is one of the greatest unknowns. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Thermoelectric** & \(R_{load}\) & \(T_{source}\) & \(T_{H}\) & \(T_{C}\) & \(T_{amb}\) & \(P\) & \(\dot{Q}\) & \(\eta\) & \(R_{HHE}\) & \(R_{CHE}\) \\
**Module** & **(\(\Omega\))** & **(\({}^{\circ}\)C)** & **(\({}^{\circ}\)C)** & **(\({}^{\circ}\)C)** & **(\({}^{\circ}\)C)** & **(\({}^{\circ}\)C)** & **(W)** & **(W)** & **(\%)** & **(K/W)** & **(K/W)** \\ \hline \multirow{8}{*}{M1} & SC & 74.23 & 61.90 & 25.47 & 16.53 & 0.00 & 37.01 & 0.00\% & 0.33 & 0.24 \\  & 1 & 76.23 & 62.50 & 24.96 & 16.42 & 0.28 & 35.34 & 0.78\% & 0.39 & 0.24 \\  & 2.2 & 75.08 & 62.75 & 24.85 & 16.57 & 0.34 & 34.22 & 0.97\% & 0.36 & 0.24 \\  & 3.2 & 75.40 & 63.19 & 24.64 & 16.56 & 0.33 & 33.38 & 0.99\% & 0.36 & 0.24 \\  & 4.7 & 75.92 & 63.73 & 24.51 & 16.44 & 0.32 & 33.36 & 0.94\% & 0.36 & 0.24 \\  & OC & 74.82 & 64.01 & 23.76 & 16.31 & 0.00 & 30.75 & 0.00\% & 0.35 & 0.24 \\  & SC & 74.23 & 61.53 & 26.11 & 16.53 & 0.00 & 39.72 & 0.00\% & 0.32 & 0.24 \\  & 1 & 76.23 & 62.32 & 25.37 & 16.42 & 0.31 & 37.07 & 0.83\% & 0.37 & 0.24 \\  & 2.2 & 75.08 & 62.51 & 25.21 & 16.57 & 0.36 & 35.76 & 1.00\% & 0.35 & 0.24 \\  & 3.2 & 75.40 & 63.02 & 25.01 & 16.56 & 0.36 & 34.96 & 1.02\% & 0.35 & 0.24 \\  & 4.7 & 75.92 & 63.59 & 24.84 & 16.44 & 0.33 & 34.77 & 0.94\% & 0.35 & 0.24 \\  & OC & 74.82 & 63.84 & 24.05 & 16.31 & 0.00 & 31.95 & 0.00\% & 0.34 & 0.24 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: For each thermoelectric module (M1 and M2) and load electrical resistance \(R_{load}\), temperatures of the heat source \(T_{source}\), the hot and cold side of the thermoelectric modules \(T_{H}\) and \(T_{C}\), and ambient \(T_{amb}\), power generated \(P\), heat flux extracted from the source \(\dot{Q}\), efficiency of the thermoelectric modules \(\eta\), and thermal resistances of the hot and cold side heat exchangers (HHE and CHE respectively). According to the previous section, it is important that the thermoelectric modules are connected to the optimal load electrical resistance. For this purpose, there exist some devices known as Maximum Power Point Trackers (MPPT) that perform this task. In thermoelectricity, the most common MPPT devices, which are also the simplest ones, adjust the output voltage of the thermoelectric modules to a value half of the open-circuit one [51]. In the present paper, each thermoelectric module has been individually connected to a Cypress MB39C831-EVB-03 Ultra Low Voltage Boost PMIC Energy Harvesting Evaluation Board [52], which works given an input voltage in the range between 0.3 and 4.75 V. As depicted in Figure 6, these boost converters are connected to a Li-ion battery. Hence, when the converter can obtain sufficient electric power from the thermoelectric modules, the charge is stared to the Li-ion battery until it reaches 4 V, when the charge is stopped. Charge restarts once the battery voltage has decreased to 3.7 V approximately. The RS Pro 18650 26H Li-ion battery pack has been used in this work [53]. On the demand side, data acquisition and communication systems are considered.