The rapid development of the industrial Internet of Things (IIoT) has transformed manufacturing processes, particularly in industries such as electronics and aerospace. While larger enterprises have successfully implemented IIoT applications to enhance productivity and facilitate smart manufacturing, small and medium-sized enterprises have faced challenges in adopting these technologies owing to financial constraints and limitations in their existing equipment. Therefore, in this paper, we propose to use Raspberry Pi (RP) as the hardware basis and the Cheng Shiu University laboratory as the research target. The approach presented in this paper involves integrating open-source packages to design both the programmable logic controller (PLC) publishing pattern and the PLC subscribing pattern. The proposed approach uses a message queuing telemetry transport (MQTT) communication protocol for transmitting Modbus transmission control protocol (TCP) register data and bidirectional data exchange with a remote monitoring system. An MQTT Broker is established to act as a bridge between the monitoring platform and the control system. A Node-RED-based IoT platform is set up to subscribe to topics from the PLC publisher for data collection. Additionally, the human–machine interface (HMI) in the monitoring system utilizes MQTT communication to publish PLC control commands, and a database is implemented for the historical analysis of monitoring data. In this paper, we aim to establish a web-based cross-platform monitoring and control system using low-cost integration through Raspberry Pi 4B embedded systems and various communication protocols. The design facilitates the IoT transformation of PLC control systems. This integrated system has broad applications in construction, production equipment, and power system monitoring to achieve power monitoring and energy conservation.