## 3 Experimental Results and Discussion  
### Hardware Implementation of Plant Monitoring System  
Figure 7 illustrates the arrangement of the proposed plant monitoring system hardware, where the left figure shows the air parameter sensor and thermal camera sensors, and the right figure shows the soil sensors. The left figure shows the distance between thermal camera #1 and thermal camera #2 is 27 cm. The RS485 to WiFi converter, air sensor, and thermal camera sensor are attached on one plate. Thus, it is easy to arrange each sensor unit for directing to the object/plant. Each RS485 to WiFi converter is connected to the soil sensor shown in the right figure (the cable is not shown). As described earlier, the sensor for air parameters (DHT22) is placed on the Plant-1 unit. The figure shows that the DHT22 sensor measures the air temperature in the monitored area, including Plant-1 and Plant-2. The mechanical system of the sensor unit is designed so that every unit can be moved downward and upward to adjust with the plant position. The height of the sensor unit can be adjusted using the tripod rod. In this work, the distance between both sensors unit is fixed, even though it could be designed as adjustable or separable. Provided with the soil sensor is a long cable for connecting the RS485 to the WiFi converter. Thus, it can be flexibly inserted into the soil in the pot or polybag. Since the soil sensor is waterproof, the plant can be watered without pulling the sensor out. The experimental setup for real-time monitoring is illustrated in Figure 8, where the left and right figures show the front and rear views of the instrument, respectively. Plant-1 is _Dieffenbachia_ planted on the typical soil placed in a pot. Plant-2 is _Veiteria zizanioides_ planted on fertilizer soil placed in a polybag. As shown in the figures, the vertical position of the plants is below the sensors; thus, the sensors are directed 30\({}^{\circ}\) downward. This arrangement causes the objects captured by the thermal camera to be the leaf, soil, pot, and concrete, as discussed earlier. \begin{table}
\begin{tabular}{c c c} \hline
**Holding Register Address** & **Variable Name** & **Unit** \\ \hline
6 & pH value & 0.01 pH \\ \hline
18 & Soil moisture value & 0.1\% RH \\ \hline
19 & Soil temperature value & 0.1 \({}^{\circ}\)C \\ \hline
21 & Soil conductivity value & us/cm \\ \hline
30 & Nitrogen concentration value & mg/kg \\ \hline
31 & Phosphorous concentration value & mg/kg \\ \hline
32 & Kalium/Potassium concentration value & mg/kg \\ \hline \end{tabular}
\end{table} 
Table 10: Modbus data addressing for JXCT soil sensor RS485 Modbus to WiFi converter. \begin{table}
\begin{tabular}{c c c} \hline
**Holding Register Address** & **Variable Name** & **Unit** \\ \hline
0–63 & Temperature value at array (0, 0)–(7, 7) of thermal camera & 0.1 \({}^{\circ}\)C \\ \hline
64 & Air temperature value of DHT22 sensor * & 0.1 \({}^{\circ}\)C \\ \hline
65 & Air humidity value of DHT22 sensor * & 0.1\% \\ \hline
66 & Average temperature value of thermal camera & 0.1 \({}^{\circ}\)C \\ \hline
67 & Otsu threshold value & 0.1 \({}^{\circ}\)C \\ \hline
68 & Background temperature value & 0.1 \({}^{\circ}\)C \\ \hline
69 & Leaf temperature value & 0.1 \({}^{\circ}\)C \\ \hline \end{tabular}  
*: Raspberry Pi Zero W #1 only.  
\end{table} 
Table 9: Modbus data addressing for Raspberry Pi Zero W.  
Figure 8: Experimental setup. Figure 7: Hardware implementation of the plant monitoring system. Since the thermal camera detects the thermal energy of an object instead of the visual appearance, the alignment of the camera position is conducted as follows. The alignment process is conducted at night, when the ambient temperature is about 25 \({}^{\circ}\)C. We then place a bulb light in front of the plants and observe the position of the hotter object (bulb light) in the thermal images. In this way, the leaf area in the image can be estimated, and then positioned in the center of the image by aligning the thermal camera.