1. Introduction The GSM network is currently the most widely covered and widely used wireless communication network in China, characterized by its wide coverage, high reliability, and low latency. Short Message Service (SMS) uses the GSM network's common control channel to transmit user packet information. Short messages are stored and sent through the Short Message Service Center (SMSC). In the GSM network, SMS exchanges user data between mobile devices (MS) and the SMSMSC in the form of datagrams. When a network failure prevents user data from reaching the other end of the mobile station (MS), the SMSMSC stores the short message and forwards it when the network failure is resolved, thus protecting user data. Each short message contains a maximum of 140 octets; when using 7-bit encoding, up to 160 characters can be sent, making it particularly suitable for remote control systems with small individual service data volumes but numerous data control points. This paper uses an oilfield pumping unit as a practical application background to introduce the architecture and specific implementation of a remote control system for a switched reluctance motor speed regulation system based on GSM SMS service. 2 System Structure The core components of this system are the AT89C51 microcontroller and the MC35i GSM wireless communication module. The peripheral circuitry is used for acquiring the operating status of the switched reluctance motor speed control system, employing an 8-bit successive approximation analog-to-digital converter. A 12-bit serial digital-to-analog converter is used for the control information input, and external memory is also included. The specific block diagram is shown in Figure 1. [align=center] Figure 1 System Block Diagram[/align] 2.1 Switched Reluctance Motor The switched reluctance motor (SRM) is the component in the speed control system that realizes electromechanical energy conversion. It is a doubly salient pole variable reluctance motor, where both the stator and rotor salient poles are made of stacked ordinary silicon steel sheets. The rotor has no windings or permanent magnets, while the stator poles are wound with concentrated windings. Two radially opposite windings can be connected in series or parallel to form a pair of magnetic poles, called "one phase." The SRM can be designed as a multi-phase structure, and there are various combinations of the number of poles of the stator and rotor. A higher number of phases and a smaller step angle are beneficial for reducing torque ripple, but the structure is more complex, and there are more main switching devices, resulting in higher costs. Therefore, the number of poles of the stator and rotor of the motor should be reasonably determined according to the application. 2.2 Switched Reluctance Motor Speed ​​Control System The switched reluctance motor speed control system is the central control unit for the switched reluctance motor. Its function is to comprehensively process speed commands, speed feedback signals, and feedback information from current sensors and position sensors, control the operating state of the main switching devices in the power converter, and detect fault signals, etc., to achieve control of the SRM's operating state. It mainly consists of a power converter, controller, position detector, etc. 2.3 Acquisition Process of SRD Operating Status The acquisition process of the SRD operating status is responsible for acquiring start/stop information, forward/reverse information, speed information, overvoltage information, overcurrent information, etc. from the motor's speed control system (SRD). For information processing, we use the 8-bit successive approximation analog-to-digital converter, TI's 4-channel serial A/D converter chip TLC0834. This chip has a configurable multi-channel multiplexer and serial input/output mode. The timing diagram of this chip shows that after the TLC0834 outputs a data stream starting with the most significant bit (MSB), it re-inputs the previous data stream starting with the least significant bit (LSB). The DI pin is only detected during multiplexer addressing, while the DO pin is still in a high-impedance state at this time. After one clock cycle, the DO pin begins to read data on the rising edge of the clock. Therefore, in designing the information acquisition circuit for the operating status of the motor speed control system, to save I/O resources, a single I/O port of the AT89C51 microcontroller is used to connect DO and DI. 2.4 Control Information Feedback Process When a fault occurs, in order to promptly adjust the motor's main controller, such as changing the motor speed, the MAX539 12-bit serial D/A chip from Maxim Integrated is selected because the speed signal is an analog voltage signal. It has the advantage of low power consumption. The MAX873 provides the reference voltage for the MAX539, with an output voltage of +2.5V, thus limiting the voltage output range of the MAX539 to 0 to +2.5V. An external proportional operational amplifier can be connected for accurate speed adjustment, thereby processing the fault information. 2.5 Communication process between microcontroller and communication module: (1) The power supply section of the communication module provides power to the module. The voltage range is 3.3~4.8V. After the MC35i module starts, after a delay of a few seconds, the module starts to search for the network. At this time, a drive current of more than 2A is required. If the drive is insufficient, the module will suddenly lose power. Therefore, the TI company's voltage regulator chip LM2576 is selected here. The voltage is stable at about 4V and the maximum current provided is 3A. This can avoid the problem of insufficient drive current when the module searches for the network. However, it was found in the experiment that the module sometimes loses power. Therefore, a large capacitor is connected in parallel at the voltage output terminal to store current and also to increase the drive current, thus solving the problem. (2) Communication process between microcontroller and communication module The microcontroller and communication module transmit information through serial communication. As shown in Figure 2, the 8 pins of the data input/output terminal of the MC35i communication module from pin 16 to pin 23 are DSR0, RING0, RXD0, TXD0, CTS0, RTS0, DTR0, and DCD0, respectively. It has fixed parameters: 8 data bits and 1 stop bit, no parity bit, and the baud rate can be selected between 300 and 115000bps. In order to communicate normally with the switched reluctance motor speed control system, 1200bps is selected as the baud rate for data transmission. The hardware handshake signal uses RTS/CTS. The module serial port supports the standard AT command set. The microcontroller's serial port needs to be connected to the MC35i module's serial port. However, since the MC35i module's serial port high level is 3.3V, while the microcontroller's serial port high level is 5V, pins 16-23 cannot be directly connected to the microcontroller. Using TI's LVC245 level conversion chip can solve this problem. Pins 24-29 of the module are SIM card pins, namely CCIN, CCRST, CCIO, CCCLK, CCVCC, and CCGND. The CCIN pin is used to detect whether the SIM card is properly inserted into the SIM card slot. If properly inserted, the CCIN pin will output a high level; if improperly inserted, the CCIN pin will remain low. The module will periodically check the SIM card during the CCCLK cycle, therefore the CCIN pin will periodically show a transition. The CCVCC pin is the power supply provided by the MC35i module to the SIM card, approximately 3.3V. To simplify the circuit, the CCIN and CCVCC pins can be always connected, keeping the CCIN pin always high. This way, the MC35i module will assume the SIM card is always present, avoiding the SIM card detection process. [align=center] Figure 2 Communication Module Peripheral Interface Circuit[/align] 3 System Function Implementation 3.1 Functional Flow The design flow diagram of this system is shown in Figure 3: The user end uses a mobile phone device, which establishes a data communication channel using the Chinese wireless communication network and the SIM card of the remote control system. It sends control information to the switched reluctance motor used in the oilfield pumping unit to control its start-stop, set speed, and other parameters; at the same time, it receives parameters such as the operating status and fault information of the switched reluctance motor, thus achieving the purpose of remote control. As shown in Figure 3. [align=center]Figure 3 System Implementation Design Flow[/align] In this system, users mainly send information to the remote motor via SMS. Specific messages represent specific commands; for example, sending "1234500" means starting the motor, and sending "12345110500" means setting the motor speed to 500 rpm. Of course, the message content can also be set to Chinese characters, such as sending "起动" (start) to start the motor, which is more intuitive and concise. This design uses this Chinese method for control. There are three modes for sending and receiving SMS messages: Block Mode, Text Mode, and PDU Mode. Block Mode requires driver support from the mobile phone manufacturer. Text Mode is simple to implement, but its biggest drawback is that it does not support Chinese characters. Currently, PDU Mode has replaced Block Mode and supports both Chinese and English SMS messages, thus having a significant advantage over Block Mode and Text Mode, and is the most widely used. However, all three modes use AT commands for sending messages. Hertz was the earliest manufacturer of modems, and those modems used AT commands. Later manufacturers' modems were compatible with Hertz's, so AT commands were necessary to send commands to the modem. The MC35i communication module is also a modem, and communication between the microcontroller and the MC35i module requires AT commands. The basic format of an AT command is: AT + command character and related parameters + carriage return, where AT is the frame header. The main AT commands used in this system are shown in Table 1: Table 1 AT Commands Used in the System. AT commands must be sent in ASIC II code, and a carriage return must be added after each AT command. The serial port response signal is also in ASIC II code format. For example, the ASCII code for 'A' is 41H, the ASCII code for 'T' is 54H, and the ASCII code for the number '0' is 3OH, etc. 3.2 Software Design The software design mainly adopts the principle of saving microcontroller resources and achieving functionality, implementing a minimal design to realize basic remote control and information functions, while leaving space for other information processing. System initialization involves setting the microcontroller's baud rate to 1200 bps (to ensure normal communication with the switched reluctance motor controller microcontroller), setting the operating mode to 1, and adding a 7-8 second delay to ensure the module can successfully search for the network. Then, the MC35i module is initialized, configured to be executed via AT commands. First, an AT command is sent; if the module returns "OK," it indicates a correct connection between the microcontroller and the MC35i module. The SMS center is then configured to send the command AT+CSCA="+8613800100500" (taking Beijing as an example). Next, the command "AT+CMGF=0" is sent to set the SMS format to PDU mode. In PDU mode, three encoding methods can be used to encode the sent content: 7-bit encoding, 8-bit encoding, and UCS2 encoding. 7-bit encoding is used to send ordinary ASIC II characters. It encodes a string of 7-bit characters (with the highest bit being 0) into 8-bit data, and every 8 characters can be compressed into 7. 8-bit encoding is often used to send data information, such as pictures and ringtones. UCS2 encoding is used to send Unicode characters. This system uses UCS2 encoding. Taking the example of the user sending the Chinese characters "起动" (start), the remote control receiving the encoding, processing it, and sending "起动成功" (start successful) back to the user, the sending process is as follows: First, the data to be sent is encoded, then "AT+CMGS=20" is sent, and the system waits to receive "<" from the network. The encoded data following this is: 0891683108101005F011000B913164216959F10008A7088D7752A86210529F. The meaning of the encoding is shown in Table 2. Table 2 Encoding Meaning Simultaneously using serial communication, programming is used to realize the control information input and motor operation status feedback of the remote control system and the switched reluctance motor controller, realizing remote information input and acquisition. The test platform of this system has been built, the functions have been realized, and the system has been tested to ensure the reliability and stability of the system, so as to reduce the failure rate in harsh working environments. 4 Conclusion The biggest advantage of using GSM short messages to realize remote control is its flexibility. It can be used in mobile environments and harsh environments. Ordinary mobile phones can be used to realize remote control and motor operation status reception. It can realize multi-point to multi-point bidirectional control and low cost[5]. Especially in harsh working environments such as oilfield pumping units, it can save a lot of manpower and material resources. However, SMS also has its shortcomings, namely, the amount of information sent is limited, and the stability is greatly affected by the network signal. Therefore, according to the actual application needs, GPRS is now being considered as the information transmission platform, and the host computer interface is used to realize remote control and information acquisition. References: [1] Cheng Longxing, Hu Xiehe, Feng Dongqin, Huang Wenjun. Remote data acquisition system based on short message. Instrumentation Technology and Sensors, 2005(1). [2] TLC0834C, 8-bit serial control analog-to-digital converter, Wuhan Liyuan Electronics Co., Ltd. [3] Li Lin, Lu Yong. Remote control based on GSM communication module. Industrial Control Computer, 2006, 19(7):25-26, 28. [4] Siemens Inc, MC35i Hardware Interface Description, 2001. [5] Zhang Guiming. Research and design of remote control and alarm based on GSM/SMS, Journal of Sichuan Normal University, 2004, 1.