## 2 Materials and Methods
### DAQ Essential Parts  
To obtain voltage, current and power curves for electrical generators, it is necessary to apply different loads to the generator. To this end, to acquire voltage and current values for a photovoltaic panel and, consequently, its characteristic curves and power values, a resistor association and switching system was developed to apply variable resistive loads to the photovoltaic panel. To facilitate connections, the resistor bank was assembled using terminal blocks for banana pin connections, and the resistors were placed on an aluminum plate, using thermal paste on their contacts to increase thermal exchange. Figure 1 details the connections between the resistors and the relay module channels. Each relay module has three connection pins: common (COM), normally closed (NC), and normally open (NO). Each resistor was connected to the NC pin of the relay module channels, as well as to each other. To establish a parallel association between the resistors, the COM pins of each relay module channel were interconnected. When the channel is activated, the connection between the COM and NC pins is established, while when the channel is deactivated, this connection is broken, and it is the COM-NO connection that becomes energized. Eight 100 W power resistors with an aluminum shell were utilized, featuring resistances ranging from 100.47 \(\Omega\) to 1.15 \(\Omega\) (Res1 = 100.47 \(\Omega\); Res2 = 47.96 \(\Omega\); Res3 = 14.84 \(\Omega\); Res4 = 7.80 \(\Omega\); Res5 = 4.83 \(\Omega\); Res6 = 4.14 \(\Omega\); Res7 = 3.50 \(\Omega\); Res8 = 1.15 \(\Omega\)). Therefore, in a scenario where channels 1 and 7 are active, the equivalent resistance provided by the system would be approximately 3.38 \(\Omega\). The resistors were connected to the positive terminal of the photovoltaic panel, while the COM pins were linked to the negative terminal. A 5 V power supply was utilized to energize the relay module, thereby preventing excessive power consumption from the load provided by the ArduinoTM board. A universal USB 5 V cell phone charger was employed to provide power, with the positive terminal connected to the JD-VCC pin and the negative terminal connected to the GND pin. A voltage divider was used to increase the maximum voltage reading value performed by the ArduinoTM controller, as the controller can only read voltages from 0 V to 5 V, which is done at the analog inputs of the board, with a resolution of 10 bits. The divider (Figure 2) consists of five resistors with a resistance of 100 k\(\Omega\) each. They are arranged into two groups: the first group has three resistors connected in parallel, and the second group has two resistors connected in series. These two groups are then connected in series with each other. In this configuration, the voltage measured across the first group (the parallel one) corresponds to one-seventh of the input voltage. Therefore, the measured voltage must be multiplied by seven, allowing the ArduinoTM to read voltages up to seven times higher than its maximum input range (35 V) for the PV panel tested with output voltage < 25 V.  
For current measurements, an ACS712 5 A current sensor was used. The sensor was powered by the ArduinoTM controller via the VCC-5 V connection and grounded via the GND-GND connection. The OUT pin, which provides the current reading of the system, was connected to an analog pin of the controller. The sensor was connected in series with the negative pole of the photovoltaic panel and the voltage divider, enabling the measurement of the current supplied by the panel. Figure 1: Connectionsbetween power resistors. The system sketch can be seen in Figure 3a, while the final assembly can be seen in Figure 3b, in which (A) is the resistor bank, (B) is the 5 V, 10 A relay module with 8 channels, (C) is the ArduinoTM Mega 2560 board, (D) the ACS712 5 A current sensor, (E) the voltage divider, and (F) a 5 V power supply (F). A DellTM Latitude D820 computer was used for data storage. All the sketches presented were made using _Fritzing_ 0.9.3b software.