## 2 Proposed System  
### IoT-Based SCADA System Configuration  
The configuration of the proposed IoT-based SCADA system is illustrated in Figure 1. In this work, we develop a SCADA system to monitor two plants, denoted Plant-1 and Plant-2. The purpose of using two plants is twofold. First, it is used to examine the performance of the sensor systems for measuring different plants or conditions. Second, it can be used to evaluate the feasibility of expanding the proposed SCADA system into a more extensive system. It is worth noting that two different plants are planted separately in the polybag or pot and placed close together in the experiments. This arrangement ensures the air conditions for both plants are the same. Thus, the air parameters can only be measured in Plant-1. Figure 1: Configuration of proposed IoT-Based SCADA system. However, the leaf temperature and soil parameters should be measured separately. As shown in Figure 1, the proposed SCADA system consists of the sensors, Raspberry Pi Zero W [50], RS485 Modbus to WiFi converter, Access point, Haiwell IoT Cloud HMI, Haiwell cloud, and a computer or smartphone for remote monitoring. The key element of the proposed system is the Haiwell IoT Cloud HMI. This device performs the SCADA function that can be accessed via the internet. Thus, it realizes the IoT-Based SCADA system. The HMI is connected to the field devices using wireless communication (WiFi) through an access point. Fortunately, the HMI unit supports the Modbus TCP protocol. Thus, it can be interfaced with other devices easily. This configuration provides a flexible arrangement of the field devices. The field devices are the sensor units, Raspberry Pi Zero W, and RS485 Modbus to WiFi converter. The sensor units are used to measure the monitored parameters. Based on the discussions in the previous section, we deal with the essential parameters and the availability of the sensor in the market, namely the leaf temperature, air temperature and humidity, soil moisture, temperature, pH, EC, and NPK. In this work, the AMG883 thermal camera measures the leaf temperature. It is connected to a Raspberry Pi Zero W using the l\({}^{2}\)C communication interface. The Raspberry Pi Zero W is used for thermal image processing, data saving, and sending to the HMI. The data are sent to the HMI using the Modbus TCP protocol wirelessly. A detailed explanation of the thermal camera specification, leaf temperature measurement method, and the data handle are provided in the next section. The DHT22 sensor measures the air temperature and humidity. This sensor is connected to a Raspberry Pi Zero W using a single-wire connection. The Raspberry Pi Zero W reads the sensor's air temperature and humidity data, store and send them to the HMI. Just as with the leaf temperature measurement, the air temperature and humidity data are wirelessly sent to the HMI using the Modbus TCP protocol. A detailed explanation of the DHT22 sensor specification, and the data handle are provided in the next section. The JXCT soil sensor [51] measures the soil parameters of pH, temperature, moisture, EC, and NPK. The JXCT soil sensor has the RS485 interface with the Modbus RTU protocol. It is then connected to an RS485 to WiFi converter (Elfin-EW11) [52] for wireless data transfer to the Haiwell IoT Cloud HMI. The reason for using the WiFi converter rather than connecting to the Raspberry Pi Zero W is that we want to evaluate the performance of the WiFi communication of the Raspberry Pi Zero W with the WiFi converter, especially when implementing the Modbus TCP protocol. A detailed explanation of the JXCT sensor specification, and the data handle are provided in the next section. The Haiwell IoT Cloud HMI is an HMI device equipped with an IoT gateway. The device has a built-in Haiwell cloud engine and cloud service. In this work, we exploit the four main features of the Haiwell IoT Cloud HMI:  
1. A low cost of about US$ 200. 2. Support of the Modbus TCP protocol for easy interfacing with the sensor systems. 3.