Design of multi-function vehicle driving status recorder

With the successful use of aircraft flight data recorders in air transportation management, vehicle driving status recorders have been widely used in many countries and regions. As early as 1990, the European Community passed legislation to install a driving state recorder on a car, and specified that the commercial vehicle must be equipped with a driving state recorder. This legislation requires its 15 member states in Europe to install the device for 9 million commercial vehicles in use within ten years. The United States, Japan, Malaysia, Hong Kong and other countries and regions have also widely used the vehicle driving status recorder. Statistics show that the use of the vehicle driving status recorder has reduced the traffic accident rate by 37% to 52%, greatly reducing casualties and property losses, and has produced significant social and economic benefits. It can be seen that accurately recording the operation process is extremely important for preventing accidents before they occur.

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In the event of a traffic accident, the vehicle driving status recorder can objectively and comprehensively record the various states of the vehicle and the operation behavior of the driver when the traffic accident occurs, and provide a real, effective and scientific original for the traffic accident analysis. Data, and can provide accident analysis function to help relevant departments quickly determine the cause of the accident to protect the legitimate rights and interests of both parties (or several parties); in normal operation, it is a powerful tool for management to strengthen supervision and management to help management The personnel fully understand the operation of the car; in the event of a vehicle failure, it can provide fault diagnosis function, providing a reliable and accurate scientific basis for the maintenance personnel to judge the fault. The promotion of the vehicle driving status recorder will play an important role in curbing serious traffic violations such as fatigue driving, vehicle overspeed, restraining driver driving behavior, preventing road traffic accidents, ensuring vehicle driving safety, and improving operational management.

1 system composition and main functions

The vehicle driving state recording system mainly consists of a vehicle driving state recorder, a handheld code reader and a management computer. The recorder is installed in the car to monitor and record the vehicle's driving data in real time. The handheld reader is composed of a handheld computer and application software for controlling and operating the recorder and reading data from the recorder through the RS232 serial port. The management computer is used to perform statistics, reports, storage, and queries on the original recorded data.

The recorder is the core of the entire system and its main functions are as follows:

(1) Real-time monitoring and recording of various status information of the car such as time, speed, idle speed, overspeed, mileage, door switch, brake status, directional light status, near high beam, engine speed, engine abnormality, oil pressure, Temperature, etc.
(2) The operation data is stored in the large-capacity serial flash memory, and the data is not lost even if the power is turned off.
(3) It has the function of timeout (fatigue) alarm and recording, which effectively curbs the driver's fatigue and ensures the safety of long-distance transportation.
(4) Hierarchical overspeed alarm function. Users can set three-level speed limit according to demand. When the vehicle is over-speed, it will receive different speed-limiting grading sound and light alarms, thus effectively curbing speeding and ensuring driving safety.
(5) The license plate number, car model, speed limit value and other data can be easily written or modified online by hand-held reader.
(6) It has a GPS interface, which can easily expand GPS time, communication, positioning, information services and other functions.
(7) A standard RS232 interface for communication with handheld readers and management computers.
(8) The management software can statistically analyze the driving speed, mileage, number of parking, parking time, speeding time, speeding time, and time of receiving and dispatching at any time, and provide various data that managers care about.

2 recorder hardware design

According to the recorder's functional requirements and work characteristics. In design, it is mainly considered from the aspects of operational reliability, accuracy of recorded data and data storage capacity. The block diagram of the recorder is shown in Figure 1. It mainly includes the MCU and its peripheral circuits, voltage, resistance, pulse and switching sampling circuit, real-time clock circuit, data storage circuit, sound and light alarm circuit, RS232 communication interface circuit and Various vehicle sensors, etc.

Logger block diagram

2.1 Single Chip Microcomputer

The C8051F005 single-chip microcomputer produced by Cygnal Company is used as the control core. In the recorder, the PCA timer array completes the V/F conversion pulse counting; the two voltage comparators realize the battery overvoltage and undervoltage detection; the on-chip temperature sensor realizes the temperature detection; the I/0 port realizes the switching quantity detection; The SPI interface controls the ISD4004-16 chip to complete the voice alarm, the real-time clock chip MAX6902 clock read and write and the data storage chip AT45DB081B read and write; the on-chip RS232 port uploads the recorded data to the host computer. It can be seen that the system control and detection can be completed by using a single chip of C8051F005 single-chip microcomputer, which greatly simplifies the system hardware design and significantly reduces the system cost.

2.2 Sensor selection

The working environment of the sensor inside the car is very harsh, so the requirements for the sensor are also very strict. These sensors must withstand temperature changes from a temperature of 40 ° C to +150 ° C, and require high precision, good reliability, fast response, strong anti-interference and anti-vibration ability, in order to accurately detect the relevant state of the car in real time, and These states are converted into electrical signals for processing by the microcontroller.

2.3 Signal detection

The output signals of the automotive sensors are generally voltage, resistance, pulse signals, and switching quantities. The detection methods of these signals are described below.

2.3.1 Voltage signal

In order to improve the anti-interference ability and detection accuracy, the voltage signal is first converted into a standard signal of 0~5V through the signal conditioning circuit, and then converted into a pulse quantity by V/F conversion. After being isolated by the optocoupler, it is counted by the PCA array of the C8051F005 single chip microcomputer. . The application circuit of the V/F converter is shown in Figure 2, in which the 3MHz pulse signal output by the active clock oscillator is divided by the 74HC393 and used as the external clock source of the AD652.

V

2.3 2 resistance signal

The resistance signal is first converted to a standard signal of 0~5V via the Wheatstone bridge, and then converted into a pulse quantity by V/F conversion, isolated by optocoupler, and finally counted by the PCA array of C8051F005 single chip microcomputer.


2.3.3 Pulse signal

The pulse signal after optocoupler isolation is directly processed by the PCA array of the C8051F005 microcontroller.

2.3.4 Switching signal

The schematic diagram of the switching quantity acquisition is shown in Figure 3. When the working state of the brake and the turn signal changes, the auxiliary contact will turn on the +12V power supply of the YX loop. At this time, the optocoupler is turned on, its output state changes, and it is read through the I/O port in the timer interrupt service routine of the MCU. Take this state, the resolution of the action can reach lms.

Switching acquisition schematic

2.4 voice alarm

When the system has an overspeed driving alarm, the high-brightness red LED light tube flashes, and the voice alarm function is activated at the same time, and the warning voice of “speeding, please pay attention” is issued.

The recorder uses a single-chip voice recording and playback circuit ISD4004-16 as a playback chip. ISD4004-16 chip operating voltage is 3.3V, single-chip recording and playback time is 16 minutes, can be divided into up to 2400 segments, sound quality is good, suitable for mobile phones and other portable electronic products. The chip uses CMOS technology and includes an oscillator, anti-aliasing filter, smoothing filter, audio amplifier, auto-squelch and high-density multi-level flash memory array. The chip design is based on all operations must be controlled by the microcontroller, the operation commands can be sent through the serial communication interface SPI; at the same time multi-level direct analog storage technology is used, each sample value is directly stored in the on-chip flash memory, so Very realistic and natural reproduction of speech, music, tone and effect sound, avoiding the quantization noise and "metal sound" caused by quantization and compression of the general solid-state recording circuit; the sampling frequency is 4.0 kHz, and the on-chip information is stored in the flash memory. It can be stored for 100 years (typical value) in case of power failure and repeated recording for 100,000 times.

In the recorder, the voice alarm content is divided into 64 segments, which can be freely combined during playback.

2.5 real time clock

In order to accurately record the sampling time of the data, the recorder uses the serial clock chip MAX6902 with SPI interface. The MAX6902 operates from a wide +2V to +5.5V supply range and is packaged in a SOT23-8 package with 31B SRAM on-chip. It features small size, simple peripheral circuitry, good operational stability, high accuracy, and low power consumption. It can meet the recorder's time requirements.

2.6 Data Storage

Since the amount of data to be recorded is relatively large, the recorder requires a large-capacity memory with a power-down memory. By comparing the flash memory AT45DB081B produced by ATMEL. AT5DB081B is a serial interface; it adopts SPI interface 0~3 mode to communicate with C8051F005 single-chip microcomputer, almost no external components are needed, high integration, large data storage, data power-down preservation; working voltage is 3.3V, working current is 4mA (only 2μA in standby mode); its main memory is 4096 pages, 264B per page, the total capacity is 1056KB (about 8Mb), and the data stored in main memory is not lost. In addition to main memory, AT45DB081B has two data caches with a capacity of 264B. The cache can be used as a buffer area for main memory exchange with external data. It can also temporarily store some temporary data. The cache can be read and written quickly and easily, but the power is lost. The data will be lost. AT45DB081B data read and write serial mode, fast read and write speed, transmission time from page to cache is about 80μs, and compatible with CMOS and TTL level input and output.

The interface schematic diagram of ISD4004-16, MAX6902, AT45DB081B and C8051F005 microcontroller is shown in Figure 4.

Interface schematic

2.7 anti-disassembly design

In order to prevent the recorder from being illegally disassembled, the system adopts a tamper-proof design. In the normal state, the next spring presses a push button switch, and the switch is closed; when the recorder housing is disassembled, the spring bounces and the push button switch is turned off. The status of the switch and the change of the recording switch state are periodically read and alarmed by the I/O port of the single chip microcomputer.

3 software design

The system software mainly completes two functions: (1) Real-time detection and recording of the driving state of the vehicle, and sound and light alarm when the fault is detected. (2) Upload the recorded data to the host computer through the RS232 port for daily management and accident diagnosis.

The software is designed according to the structured programming scheme, and the whole program is divided into several program modules according to functions to facilitate debugging and inspection. Programming in Keil C51 language. After editing, compiling, connecting and debugging in the KeilμVision2 V2.05 integrated environment, the software in this design downloads the program directly to the C8051F005 MCU (ISP) through the JTAG interface. The program mainly includes: main program, analog quantity acquisition program, switch quantity acquisition program, pulse quantity acquisition program, data storage program, clock processing program, fault processing program, voice alarm program and serial communication program.

4 system reliability design

As a vehicle driving state recorder, the working environment inside the car is very bad. Therefore, how to ensure the stability and reliability of the system is very important.

Although the system hardware has been carefully designed, such as multi-layer printed boards, reliable component selection, optocoupler isolation of input and output, power input and output filter, hardware watchdog, etc., has a strong anti-interference Role; but because the working environment of the recorder is more complicated. In order to ensure the absolute and reliable operation of the system, the above measures are still insufficient, and it is necessary to comprehensively consider the software design to enhance the comprehensive anti-interference ability of the system.

The direct result of the system encountering interference is that the program runs away. In software design. Mainly from the software modular design and event-driven mode, instruction redundancy and software traps, multiple copies of software important variables, software reentrant design and digital filtering, etc., to enhance the system's comprehensive anti-interference ability. Practice has proved that these measures have achieved good results.


The recorder strictly follows the requirements of automotive electronic products and fully considers the interior environment (such as electromagnetic interference, vibration, temperature, humidity, etc.), in various steps such as circuit principle design, electronic component selection, structural design, and connector selection. They are strictly in accordance with the corresponding electronic equipment standards and have passed various environmental tests. Since it was put into operation, it has achieved good results and can fully meet the needs of real-time recording of vehicle driving data.

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