## 4 Economical Miniaturized Arduino-Based Metamaterial Setup
### Arduino Meta Setup
#### 4.2.4 Evaluation of Kit by Load Variations  
Evaluation of the kit was carried out by conducting eight tests one after another, on eight different external resistors for various axial load increments by placing weights of 0.5 N, 2.5 N, 4.5 N, 6.5 N 8.5 N, 10.5 N, 12.5 N, 14.5 N, 16.5 N, and 18.5 N on top of the LSP sensor. Similar to the previous case, first a 0.5 N weight was gently placed on top of the sensor. The program code C was executed for the time window of 5 s during which 50 digital values were recorded into another Microsoft excel file as done previously. The mean digital output value was calculated for the load, and the same experiment was repeated by increasing the load. The entire process was repeated by changing the external resistors, and a graph of the obtained mean digital output values was plotted as shown in Figure 9. Table 1 shows the range of digital values from the smallest to the largest for all the resistors between the applied loads. There was no change in the output digital value when higher resistor was adopted for an increase in load. For example, the digital value does not have significant change when the load is above 2.5 N for the 100 k\(\Omega\) resistor. Thus, such a resistor may not be suitable for determining the magnitude of load but will be suitable for mere detection of an applied load. On the  
Figure 8: Optimization of external resistor for user desired force measurement system. (**a**) Schematic potential divider between external resistor and internal resistor; (**b**) experimental setup and circuit diagram; and (**c**) Digital values Vs external resistor.  
other end of the spectrum, a similar trend can also be seen for the lower resistors, say 10 \(\Omega\), where there was a little change in the digital value for applied loads above 0.5 N. From the table, it is difficult to identify the magnitude of the applied load, as the digital output value remained more or less the same throughout. Furthermore, its digital curve (in color red) is at the bottom which is very close to the 0 value, i.e., parallel to the \(X\)-axis. This means that for lower resistors, the kit is not sensitive to either the presence or the magnitude of an applied load. However, the mean output digital value increased when the load increased especially for 510 \(\Omega\) (brown color) and 1 k\(\Omega\) (dark green color) as shown in the figure. Similarly, the difference of the maximum and minimum mean digital output value for the 510 \(\Omega\) and 1 k\(\Omega\) resistor is 418.88 and 515.15 respectively, which is considerably higher compared to the other resistors given in the table. The trend lines with associated mathematical expression and their regression values are also given in the figure. This wide range of output enables these resistors to be more sensitive, which allows detection of even a small load and any minor changes. Thus, the optimum resistors can be considered between 510 \(\Omega\) and 1 k\(\Omega\).  
Such easy to build portable SHM setups are not only economical but offers a variety of programming options. Irrespective of whether such kits find any place in physics or medicine, they offer a variety of options for SHM of CMA engineering structures.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Resistor** & **10 \(\Omega\)** & **100 \(\Omega\)** & **510 \(\Omega\)** & **1 k\(\Omega\)** & **5.1 k\(\Omega\)** & **10 k\(\Omega\)** & **51 k\(\Omega\)** & **100 k\(\Omega\)** \\ \hline Range of digital value & & & & & & & \\ (difference between min to & 19.86 & 158.08 & 418.88 & 515.14 & 573.42 & 428.28 & 195.24 & 122.30 \\ max applied load) & & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Range of digital value for load range between 0.5 N to 18.5 N.  
Figure 9: Force variation Vs. Load for various resistors.