Design of universal industrial wireless remote control system based on single chip microcomputer and PLC

    1. Introduction

    Industrial wireless remote control system can digitally process the control instructions of the operator or machine, transmit them to the remote receiving system through the transmitting system, and then convert them into control instructions through decoding to realize the control of various mechanical equipment. At the same time, it requires the ability to resist interference in industrial environments with strong magnetic fields, strong electric fields and complex radio signal environments. Industrial radio technology is a comprehensive technical system that combines modern digital communication technology with traditional radio communication.

    In actual industrial sites, especially for mobile equipment and complete sets of equipment, if a wireless remote control system is used, the operator only needs to carry a lightweight transmitting system, move freely and choose the best (safe) visual position for operation, eliminating the potential accidents caused by unclear vision, harsh environment or improper command, ensuring safe operation, and various operations can be undertaken by one person without the need for command from others, saving human resources. The operator makes independent judgments, and the accuracy and consistency of operations are significantly improved compared with the past, thereby greatly improving production efficiency.

    2. System design

    The wireless remote control system can be divided into a transmitting system and a receiving system. We make the transmitting system the transmitting end and the receiving system the receiving end, and perform data transmission and communication through the wireless data transmission module.

    Various buttons and joysticks for on-site control are designed on the transmitter of the remote control system, so that the remote operation transmitter can control the operation of the on-site equipment. By pressing the operation button on the transmitter control panel, the microcontroller will start the corresponding serial port transmission program after detecting it. The wireless data transmission module transmits data, and the receiving end controls the operation of the on-site equipment. It is composed of a wireless data transmission module, PLC and on-site equipment. When the wireless data transmission module receives the data from the transmitter, it uses the free port communication method to start the corresponding PLC control program to control the operation of the on-site equipment.

    2.1 MCU transmitter design

    The overall design of the transmitter adopts the structure shown in Figure 1.

Figure 1 Transmitter hardware configuration diagram

    The single-chip microcomputer module uses the xc164 single-chip microcomputer, which is a 16-bit microcontroller product of Infineon. Its excellent structure, efficient instruction set, and continuously expanding and updating product lines make it widely used in automotive electronics, industrial control and information technology. This series of single-chip microcomputers has rich interface modes, such as 14-channel 10-bit AD converter, synchronous/asynchronous serial channel USART, high-speed synchronous serial channel SPI, CAN module, 79 IO pins, etc., and can form a communication network with various devices. At the same time, this series of single-chip microcomputers is suitable for harsh industrial environments, and the industrial temperature can be between -40 and 125℃. In view of the functions of our transmitter, at the same time, the remote control has the advantages of stable working performance and easy function expansion. Taking into account the on-site environment of industrial applications.

    The project design adopts the following method: for example, when the switch button is pressed (such as start, stop, etc., different control systems have different function buttons), the microcontroller detects the change in its port potential, starts its corresponding program, and then sends the corresponding data to the wireless data transmission module through the serial port. The program flow chart shown in Figure 2 can be used for programming the microcontroller button input program processing.

Figure 2 Flowchart of wireless transmission program

    2.2 PLC free port receiving end design

    The overall design of the receiving end adopts the structure shown in Figure 3.

Figure 3 Receiver hardware configuration diagram

    The on-site operation equipment is controlled by PLC. The PLC program can control various operation modes of the equipment. Siemens S7-200 has one or two RS-485 standard interfaces, so the wireless data transmission module can be directly connected to the RS-485 interface of the PLC. After the receiving module receives the data, the PLC starts the corresponding interrupt program and starts to run the corresponding control program. [page]

    The communication port of the S7-200 series PLC supports multiple communication protocols, and two of them can be used here. One is the Siemens PPI master-slave protocol, which allows the master station to directly issue instructions to the slave station, that is, the PLC in the control system, to control the ports and functions of the slave station. This method is simple to program the PLC and does not require modification of the original slave station program. However, the PPI protocol is not a public protocol. Reference 4 mentions a method of obtaining the PPI protocol through serial port monitoring and using the master station programming to control the slave station. Another communication mode is the free port mode, which uses a custom PLC program to control the communication port of the S7-200 CPU and uses the user-defined communication protocol to achieve communication with the outside world. This mode supports ASCII and binary protocols. The free port mode is simple and flexible to use, but it requires special programming for the PLC. Because the amount of data required for wireless remote control is not large, the free port communication mode was selected through comparison to transmit commands and feedback information between the handheld operator and the PLC in the form of ASCII code. A special wireless control program is written in the PLC to realize data communication and control of the robot under wireless control. We use the free port communication of S7-200. Using free port communication, users can customize the communication protocol to communicate with the intelligent device used.

    After adopting the free port communication protocol, the receiving end receives the data and transmits it to the PLC through the wireless data transmission module, and starts the corresponding program. The program is compiled using the flow chart shown in Figure 4.

Figure 4 PLC receiving flow chart

    2.3 Wireless data transmission module

    (1) zf02 series wireless data transmission module: The transmitter and receiver use wireless data transmission modules for data communication. There are many types of wireless data transmission modules on the market. According to actual needs, we directly use the zf02 series wireless data transmission module produced by Shanghai Zhaofu Communication Technology Co., Ltd. Its main features are: carrier frequency: 433mhz, 450mhz, 470mhz, 868mhz; a variety of optional communication interfaces: rs-232, ttl, rs-485; transmission rate: 1200, 2400, 4800, 9600, 19200, 38400bps; integrated transceiver, half-duplex working mode. zf02 is very suitable for the wireless remote control system designed in the project. Its appearance is shown in Figure 5.

Figure 5 Interface and dimensions

    (2) The wireless data transmission module has three communication interface modes: a TTL level serial communication interface, which can be directly connected to the serial pin of the microcontroller chip; a standard RS232 interface and a standard RS485 interface, where the standard RS232 interface and the standard RS485 interface are switched by jumpers. The Siemens S7-200 series has one or two RS485 standard interfaces, which can be directly connected to the 485 interface of the wireless data transmission module.

    3. Conclusion

    This system design is a universal design, which can be specifically designed for specific equipment by modifying the corresponding input function buttons or joysticks at the transmitter end, and modifying the software programs of the microcontroller system and the PLC system at the same time to make them meet the operational function requirements of the on-site equipment.