Abstract: Data acquisition and analysis systems are of great significance to the development of AMT systems. This paper introduces an automotive AMT data acquisition and analysis system based on serial communication and virtual instrument technology, and elaborates on the system's working principle and software and hardware design. Keywords: AMT, data acquisition, serial communication, virtual instrument 0. Introduction AMT (Automated Mechanical Transmission) is a mechanical automatic transmission that replaces the manual operation of clutch disengagement, engagement, gear shifting, and engine synchronization by adding a microcomputer-controlled automatic operating mechanism without changing the original mechanical transmission clutch structure. It ultimately automates the entire gear shifting process. It combines the advantages of AT automatic transmission with the advantages of high efficiency, low cost, simple structure, and ease of manufacturing of the original manual transmission (MT). The basic control principle of the system is shown in Figure 1. The AMT system is a complex multi-input multi-output control system with many parameters that change rapidly and have short time histories. Some phenomena that are difficult to observe manually or with ordinary testing instruments, especially the complex dynamic process of multiple control parameters changing instantaneously, can only be fully and meticulously analyzed using a data acquisition and analysis system. The selection of multiple design schemes for automatic transmission control systems, the determination of hardware such as sensors and actuators, and especially the design and debugging of software, all rely on extensive testing and trial runs. With the development and continuous improvement of automatic transmission theory, in order to more rationally determine the shifting rules and improve the adaptability of the automatic transmission system to different drivers, roads, and vehicle conditions, a large number of tests are needed to collect a certain amount of data as a basis for design. Even with a large amount of data, processing and analysis are still required to obtain the performance indicators that technicians care about. Completing these tasks is very time-consuming for humans. A data acquisition and analysis system can automatically process and analyze the collected data, quickly obtain useful test results, and provide them to designers in a clear and intuitive way. Because on-board data acquisition and analysis systems are of great significance to the development of AMTs, we developed such a system for the research and design of AMTs. 1. System Composition The data acquisition system can be implemented in two ways: one is a single host computer method based on a data acquisition card, and the other is a method based on the AMT electronic control unit (ECU) as the lower computer and the PC as the upper computer. Since the signals from the data acquisition system are also used by the AMT's electronic control unit (ECU), to simplify the system structure, the lower-level computer of the acquisition system and the AMT's control system can share some hardware, with a serial communication interface circuit added on top of that. Because PCs have powerful functions and rich software, we chose a common portable PC with a Windows XP operating system as the upper-level computer. The lower-level computer is responsible for data acquisition and conversion, transmitting the data to the upper-level computer via serial port. The upper-level computer is responsible for classifying, storing, and analyzing the received data, displaying the data of interest to the researchers. 2. System Hardware Design The system hardware mainly consists of the following parts: sensors, signal conditioning circuits, lower-level computer (ECU), serial communication interface circuit, power supply circuit, upper-level computer (PC), and some necessary peripheral circuits. The block diagram is shown in Figure 2. 2.1 Sensor Selection and Signal Conditioning Circuit Design The signals of the data acquisition system are generated and transmitted by sensors; the sensors are the source of the data acquisition system. The appropriateness of sensor selection will have a significant impact on data acquisition and subsequent analysis. Since the signals from the data acquisition system are also used by the AMT electronic control unit (ECU), the selection of sensors must take into account the requirements of both the AMT control system and the data acquisition system. The AMT system is a multi-signal input system, which can be broadly categorized by signal type as: analog, digital, and frequency signals. Correspondingly, sensors are also categorized as analog sensors, digital sensors, and frequency sensors. Analog signals include accelerator pedal displacement, gear shift position, throttle opening, and clutch displacement, which use rotary potentiometers; digital signals include start, reverse gear selection, and brake pedal signals, which use ordinary buttons; frequency signals include engine speed, input shaft speed, and output shaft speed (vehicle speed), which use Hall effect sensors. The signals output from the sensors cannot be directly used by the ECU and must undergo appropriate processing. The processing circuits differ for different signals. Analog signals are susceptible to interference during transmission after being introduced into the control system via cables. Before being introduced into the analog input pins of the A/D conversion module, they should be filtered, amplified, and limited to ensure they are within the amplitude range that the ECU's analog-to-digital conversion module can process. Digital signals are connected to the ECU data bus after opto-isolation. The frequency signal needs to be filtered, clamped, amplified, and shaped to become a pulse signal that the microcontroller can process. 2.2 Selection of the Lower-Level Machine and Design of the Communication Interface The lower-level machine is the core of data acquisition. It not only needs to complete the corresponding control of automatic gear shifting but also the task of data acquisition. Its selection is crucial to the quality of the entire AMT control system. We chose the 16-bit MC68HC912BC32 microcontroller produced by Motorola. It has 1000 bytes of RAM, 768 bytes of EEPROM, 32000 bytes of FLASH, as well as a timer TIM module, an analog-to-digital converter (ATD) module, serial interface SCI and SPI modules, a pulse width modulation (PWM) module, and the CAN bus communication interface widely used in vehicle electronic control systems. Its excellent performance provides strong support for simultaneously completing automatic gear shifting control and on-board data acquisition tasks. Both the lower-level machine MC68HC912BC32 and the upper-level PC have serial interfaces, and communication between them is completed through the serial port. However, the SCI port of the MC68HC912BC32 uses CMOS level, while the PC's serial port is designed according to the RS-232 standard. The RS-232 standard uses negative logic levels, i.e., "-3 to -15V" is "1" and "+3 to +15V" is "0". The two levels are incompatible. Therefore, the system uses the MAX232 as the interface chip, and the connection circuit is shown in Figure 3. 2.3 Power Supply Circuit The car's power supply is +24V, while the microcontroller requires +5V. The system uses a DC/DC converter to convert the car's +24V to +5V. Simultaneously, the ground of the data acquisition system is isolated from the car's power supply ground to avoid mutual interference and ensure the reliability of the acquisition system. 3. System Software Design Hardware is the foundation of the system, while software is its soul. The software of the data acquisition system mainly consists of two parts: one is the lower-level computer's data acquisition and transmission software, written in Motorola microcontroller assembly language; the other is the upper-level computer's data reception, data analysis, processing, and monitoring software, written using the LabVIEW virtual instrument development platform. 3.1 Lower-level Software Design Since the lower-level computer runs the data acquisition and transmission program while simultaneously running the automatic gear-switching main control program, the program primarily uses interrupt-driven operation to ensure coordinated and efficient system operation. 3.1.1 Data Composition Asynchronous serial data transmission is based on bytes, with one start bit and one stop bit, and no parity bit, forming a frame. Multiple bytes form a data block, and consecutive data blocks form a data stream. Data blocks are separated by synchronization bytes. The upper-level computer uses synchronization bytes to locate the start position of the data frame. The analog quantities in the system are 10-bit precise during A/D conversion. Frequency signal acquisition uses an 8-bit pulse accumulator, and switch quantity acquisition uses an 8-bit I/O port. All system signals are sampled once every 10ms. The data acquired within 10ms is packaged into a data frame. Each data frame consists of one synchronization byte and 16 data bytes, totaling 17 bytes. This requires sending 1700 bytes per second, plus one start bit and one stop bit for serial transmission, resulting in 17000 bits/second. Therefore, a baud rate of 19200 for serial communication is sufficient to meet the requirements. 3.1.2 Data Acquisition Software Design: The acquisition of each signal is completed by a software timer, which generates an interrupt at regular intervals. This software interrupt is used to initiate the sampling, conversion, and reading of the input signal, and sends the first byte of the data block to be sent to the serial port transmit register, thereby starting the serial port interrupt service routine. The software timer interrupt service routine is shown in Figure 4. 3.1.3 Serial Data Interrupt Transmission Program Design: After the microcontroller writes the byte to be sent to the serial port transmit buffer register, the relevant serial port hardware circuit automatically performs parallel-to-serial conversion of the byte and sends the data outward. After transmission is complete, the microcontroller generates a serial port transmit interrupt and sends the next byte to be sent to the serial port transmit buffer register. The program is shown in Figure 5. 3.2 Host Computer Software Design: The host computer software includes a communication module for data transmission; a data conversion and display module; an automatic data storage module; and a data analysis module. It is written using the LabVIEW virtual instrument technology development platform. 3.2.1 Introduction to Virtual Instruments and LabVIEW Virtual instruments (VI) are a new and dynamic type of instrument formed by the integration of computer technology into the field of instrumentation. In virtual instruments, computer software technology and testing systems are more closely integrated into an organic whole. Their widespread application represents a revolution in testing instrument technology and a new milestone in the field. Virtual instruments, based on the concept that "software is the instrument," offer greater flexibility and adaptability compared to traditional instruments. Once the basic hardware is determined, only the software needs to be changed to achieve different functions and meet the requirements of different occasions. Virtual instrument application software integrates all the instrument's functions, including data acquisition, control, data analysis, result output, and user interface, allowing some hardware or even the entire instrument to be replaced by computer software. LabVIEW (Laboratory Virtual Instrument Engineering Workbench), a virtual instrument development platform provided by National Instruments (NI), offers a completely new programming method—G language (graphical language)—replacing traditional text-based programming languages, greatly improving programming efficiency. It also has a powerful library of data analysis, processing, storage, and display functions. In addition, LabVIEW provides a powerful VISA library. VISA (Virtual Instrument Software Architecture) is a general term for standard I/O function libraries and related specifications used for instrument programming. The VISA library resides in the computer system and serves as a software layer connection between the computer and the instrument. It is a high-level API (Application Programming Interface) that controls the instrument by calling lower-level drivers. The hierarchical structure of NI-VISA is shown in Figure 6. 3.2.2 Communication Module Design The communication module includes configuring the serial port and reading serial port data. The serial port configuration is achieved by calling the serial communication node in the VISA library, and must be consistent with the communication protocol set on the lower-level machine. The VISA Configure Serial Port node is used to initialize the serial port. The main parameter settings are as follows: VISA resource name: Serial port resource name, which can be COM1 or COM2; baud rate: Baud rate, 19200; data bit: Number of data bits in one frame, 8 bits; parity: Parity bit, set to none; stop bit: Stop bit, 1. The VISA read node is used to read serial data. Since LabVIEW can only read characters, the "String To Byte Array" node must be called after reading the data to achieve correct conversion between strings and numbers. Data blocks are separated from the data stream based on synchronization bytes, data frames are separated from the data blocks, and then valid two-byte data is extracted from the data frames and combined to form a data array. 3.2.3 Design of the Data Conversion, Display, and Storage Module: Data conversion involves performing necessary transformations on the data read from the serial port to obtain data with actual physical meaning, such as restoring A/D converted data to actual physical quantities, or converting frequency signals into actual rotational speeds. This can be easily achieved using the data processing functions provided by LabVIEW. The converted data is sent to the display VI, and displayed in real-time using a gauge or waveform chart. Simultaneously, the data is automatically stored in the background, saved as files with file identifiers such as time and operating conditions for future retrieval and analysis. 3.2.3 Data Analysis Module Data analysis involves statistically analyzing, monitoring, and interpreting performance indicators of the AMT system (e.g., clutch engagement and disengagement time during gear shifting, impact and slippage work during gear shifting, etc.). Analysis allows for the evaluation of the rationality of the gear shifting process, providing intuitive, fast, and precise quantitative basis for improving system performance, determining specific parameters of the control software, and optimizing the software's control strategy. LabVIEW can display performance indicators in real-time charts and can also open stored files for post-event analysis using waveform graphs. 4. Conclusion This data acquisition and analysis system has advantages such as a user-friendly interface, ease of use, and rich functionality. Extensive on-vehicle testing demonstrates that the system's hardware and software operate stably and reliably, meeting the requirements of various vehicle operating conditions. It provides a favorable guarantee for improving the control strategy, adjusting parameters, and continuously optimizing the performance of the AMT system. References: 1. Ge Anlin. Automatic Transmission Theory and Design of Vehicles. Machinery Industry Press. 2. Yang Leping, Li Haitao, Yang Lei. LabVIEW Programming and Application. Electronic Industry Press. 2005. 3. Yang Guotian, Bai Yan. *Motorola 68HC12 Series Microcontroller Principles, Applications and Development Technology*. China Electric Power Press. 2003. 4. Shao Beibei. *Online Development Methods for Embedded Applications of Single-Chip Microcomputers*. Tsinghua University Press. 2004. Author Biographies: Xue Dawei, Postgraduate student, School of Electrical and Automation Engineering, Hefei University of Technology, Research direction: Control Theory and Control Engineering. Mailing address: Room 393, Hefei University of Technology, E-MAIL: [email protected]. Kong Huifang, Associate Professor, Research direction: Control Theory and Control Engineering, Power Electronics.