## 4 Hardware Configuration of the Proposed WAS  
The range covered by the individual node and the total area of the crop field can be set based on the number of nodes to be deployed in the field. Table 2 presents the hardware for the sensor node of the proposed WAS. Figure 2 shows the hardware of the sensor, router, and coordinator nodes. It presents a simple hardware implementation of the WAS, which involves minimal interface and connection between sensors to the microcontroller and the wireless links. The digital humidity-temperature (DHT11) sensor and the soil moisture sensor require only three wires for a physical interface with the microcontrollers: (i) supply voltage, (ii) ground, and (iii) output data. The first two wires are used to power the sensors by +5 V, whereas the third wire is the analog and digital serial output signals for the soil moisture sensor and DHT11, respectively. The microcontroller of the sensor and router nodes communicates with the Zigbee wireless protocol through a single-wire data bus.  
Figure 1: WSN topology of the proposed WAS for precision farming.  
The sensor and router nodes are fixed on a surface that is 1.5 m above the ground (Figure 3), which is the recommended height in [39], to avoid the effect of the Fresnel zone or signal reflection. The sensor and router nodes in the tested area are powered by a battery. The coordinator node is connected to a laptop/PC in the base station. Therefore, this node is unaware of the energy supply. The PC is equipped with graphical user interface (GUI) software to monitor the climate conditions in the farm field. The sensor and router node structures are designed to work day and night. At daytime, the components, sensors, microcontroller, and XBee S2C are powered by solar energy. Furthermore, a solar cell provides energy to charge the batteries of the sensor and router nodes. The solar panel is positioned in front of the sensor node box at a low inclination angle (20\({}^{\circ}\)-30\({}^{\circ}\)) to orient the solar cell panel relative to the sun. In addition, two power reduction algorithms (i.e., sleep/wake and _SWORD_) are adopted to further reduce the power consumption of the sensor and router nodes. At nighttime, the components only use battery energy as supported by the two power reduction algorithms. For WSN simplicity and to reduce the complexity of the proposed WAS, one sensor node, one router node, the main router node, and the coordinator node are practically implemented to monitor the climate conditions in the farm field.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Number** & **Hardware Type** & **Description** \\ \hline
1 & Temperature and humidity sensor & DHT11 \\
2 & Soil moisture sensor & YL-100 \\
3 & Microcontroller & Atmega 328p as standalone \\
4 & Wireless protocol & Zigbee based on Xbee S2C [40,41] \\
5 & Power systems & Li-ion battery (7.4 V/2600 mAh) \\
6 & Power solar cell & KINGRO-004V (12 V/5 W) \\
7 & DC–DC converter & LM 2596 \\
8 & Charger controller & PWM-LS2024E \\ \hline \hline \end{tabular}
\end{table}
Table 2: Major components of the sensor node for the WAS hardware.  
Figure 3: Sensor node installed at the farm.  
Figure 2: Hardware of the WAS: (**a**) sensor node, (**b**) router node, and (**c**) coordinator node.