## 3 Experimental Evaluation
### Testing ECG Signal  
As shown in Table 9, when there is no light, the device operates stably for a short time only 2 s, so to make the device more stable, it is necessary to have a source of solar cells capable of creating large capacity or stable light source. In this design, we use a solar panel with a small size (Figure 5a). In the tests, we performed in an environment with almost no natural light and we used an artificial light source with a total capacity machining of 27 W for solar panels.  
Before using the ECG device in this test with volunteers, we had tested the device's accuracy with standard devices. The standard device used here is the function generator model Tektronix AFG3252 signaling with a descriptive form close to the human heart rate signal and oscilloscope MSOX2024A to  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Mode** & **Status** & **Current Consumption (\(\mu\)A)** \\ \hline
1 & Active (PIC, RN4020, ADS1293) & 2100 \\
2 & Active (PIC, RN4020), Sleep (ADS1293) & 1900 \\
3 & Active (RN4020), Sleep (PIC, ADS1293) & 500 \\
4 & Sleep (PIC, RN4020, ADS1293) & 40 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Consumption current in working modes.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Number** & **Power Source** & **Used Time (s)** \\ \hline
1 & Supercapacitor 0.47 F - 5.5 V (1.25 mWh) & 2.1 \\
2 & CR2030: 3 V - 220 mAh (660 mWh) & 1112 \\
3 & NCR18650B: 3.7 V - 3400 mAh (12,580 mWh) & 26,484 \\ \hline \hline \end{tabular}
\end{table}
Table 9: Used time of ECG device with differences sources.  
After experimenting with the device generator above with good results, we continued to test the ECG device with a volunteer. Before conducting ECG signal measurements, we set up the system. Volunteers were sitting in a chair and leaning back in a comfortable state. We pasted 4 electrodes on the volunteer and these electrodes are connected to the ECG device as described in Figure 11. During the experiment, the volunteers were quite comfortable and did not have strong movements before conducting the experiment.  
The test with high sampling frequency Fs = 2133 Hz waveform of the ECG signal is described in Figure 11. With the data in this test, we applied the high pass filter with cutoff frequency of 0.04 Hz and low pass filter with the parameters in Table 11. From this wave, we can see that the ECG signal consists of many noise signals, especially the 60 Hz power line noise signal. After applying filters, we obtained relatively clear and accurate ECG signals. From this signal, we can understand the situations of some features in the human body, such as rhythm or muscle contraction rhythm.  
Additionally, we also tested the device with low sampling frequency Fs = 100 Hz. The test results are shown in Figure 12. In this test, we applied the high pass filter with a cutoff frequency of 0.04 Hz and a low pass filter with the parameters in Table 12. Here we can see that the ECG sampled the signal, and thus, we can determine the volunteer's heart rate as well as the QRS parameters. However, due to the low sampling frequency, no interference with ECG signals was shown.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Low Pass Filter** & **FIR** \\ \hline Design method & Window \\ Type of window & Chebyshev \\ Filter order & 500 \\ Cut-off frequency & 40 Hz \\ \hline \hline \end{tabular}
\end{table}
Table 11: Low pass filter parameters at sampling frequency 2133 Hz.  
Figure 11: Setup system measurement ECG signal.  
Figure 12: Cont.  
Figure 12: ECG signal before and after filter with sampling frequency 2133 Hz: (**a**,**b**) left arm to right arm signal, (**c**,**d**) left leg to right arm signal, and (**e**,**f**) left leg to left arm signal.