introduction
In recent years, people have been paying attention to and studying the driving safety of cars on mountain roads. As a new active safety system, the early warning system will further increase the safety of vehicles, reduce the incidence of accidents, and continue to meet the growing market.
The overall plan design of the early warning system
This system is based on the vehicle-road driving safety model of the mountainous region of the car, and takes the vehicle mountain road driving safety early warning system as the research object to achieve signal collection, conditioning, transmission, and finally achieve the purpose of early warning. To achieve real-time early warning of vehicles, it is necessary to collect real-time collection of vehicle operating conditions, road operating conditions and surrounding environmental conditions, etc., and determine their operating status based on the collected data. After the early warning algorithm is performed by the processor, the final Make corresponding voice prompts to ensure the driver's safe driving and achieve the purpose of reducing traffic accidents.
Through the study of the purpose of this system, the hardware circuit of the early warning system can be roughly divided into three parts: input module (signal determined according to the safety model, sensor acquisition), digital signal processor (DSP) module and output module (voice Alarm prompt module). Among them, take the processor as the core, and connect the signal input and output through the bus and the interface circuit. These modules make up the overall block diagram of the mountain road vehicle driving safety warning system, as shown in Figure 1.
Figure 1 Block diagram of the system
The input module of the early warning system includes collecting signals and processing the collected signals. The signals that need to be collected in this system include vehicle operating status signals (such as vehicle speed, etc.), road parameters (such as slope, etc.) and surrounding environmental conditions (such as temperature, etc.). The difference between these signals requires different sensors and sensor adjustment circuits. The circuit design for the acquisition and processing of vehicle speed signals will be briefly described later.
Digital signal processors (DSPs) are widely used due to their high performance and flexible programmable advantages. Various companies produce a wide variety of DSP chips for different applications. Therefore, when designing DSP systems, it is necessary to rationalize the DSP chips. Choose a question. The TMS320 series DSP produced by TI is currently the most influential mainstream DSP product in the world. The chip has the characteristics of low price, easy to use, and powerful functions. The DSP chip TMS320LF2407A selected by this system is the motion control DSP chip with the highest integration and the strongest performance in the world today. It lays a good foundation for extending its control function after successful warning.
The output module of the early warning system is mainly the voice prompt module. A voice prompt signal is issued some time before the danger may occur, early warning the driver to correctly control the car, and make positive protective measures to achieve the effect of reducing the occurrence of traffic accidents.
Early warning system hardware design
The driving safety model of mountain roads is mainly to analyze the driving conditions of vehicles on long downhills, uphills and bends of mountain roads. There are many signals to be collected, and their input signal circuits are also different. The following is a brief introduction to the driving speed of vehicles Signal collection and processing circuit design.
Design of adjusting circuit of speed sensor
The measurement of automobile driving speed adopts Hall switch sensor. In this paper, the Hall sensor model 2SS52M is selected. According to its main technical parameters, the 2SS52M Hall sensor is a voltage sensor with an output voltage range of 0 ~ 3.3V, which does not exceed the DSP A / D conversion voltage. However, in actual application, because the Hall sensor is usually installed on the rotor shaft of the motor, it is inevitably subject to strong electromagnetic interference. In order to improve the anti-interference performance of the system, the signal it sends needs to be processed after high-speed photoelectric isolation. In addition, in order to make the quadrature-encoded pulse sent by the Hall speed sensor a standard sinusoidal waveform, a 74LVC14A chip is used to shape the signal, and the shaped waveform is input to the QEP pin of the DSP. The circuit connection is shown in Figure 2. Since the 74LVC14A chip is a six-reverse Schmitt trigger, it can transform non-rectangular waves into rectangular waves. The shaping principle is shown in Figure 3.
Figure 2 Hall sensor adjustment circuit
Figure 3 Using Schmitt trigger to shape the pulse
Hardware design of voice prompt module
The voice prompt is realized by the voice chip ISD1730 driving the speaker.
When the car is running on a mountain road, the input module collects the required signal information, and the controller module comprehensively calculates and judges its safety level. If it is not safe, then the DSP (TMS320LF2407A) module outputs the control voice module, and the audio output by the voice chip The signal is output through the power amplifier circuit to realize the early warning function. DSP (TMS320LF2407A) internally integrates SPI interface, which can facilitate serial communication with ISD1730. The interface circuit between TMS320LF2407A and voice chip is shown in Figure 4.
Figure 4 Interface circuit between TMS320LF2407A and voice chip
It can be seen from Figure 4 that the DSP and the voice chip ISD1730 are connected by four wires, the SPISTE pin of the DSP is connected to the chip select signal SS of the ISD1730, this pin controls whether the ISD1730 voice chip is gated, and the SPISIMO tube of the DSP The pin is connected to the serial data input terminal MOSI of the ISD1730. This pin provides the control command word and playback address for the voice chip. The SPIMISO pin of the DSP is connected to the serial data output terminal MISO of the ISD1730. The voice chip received by the DSP from this pin The returned signal, the SPICLK pin of the DSP is connected to the serial clock input terminal SCLK of the ISD1730. This pin provides the clock signal for the voice chip ISD1730. The Rosc terminal of the ISD1760 is connected to the 80K resistor to ground, and the sampling frequency can be set to 8KHz, the maximum The recording time is 60s; before the system realizes the early warning, you can use the recording software to record the required .wav format sound source file, and then input the sound source file into the computer ’s CoolEdit or Goidwave software for editing, and then pass the required content through the ISD1700S The voice programming copying machine is recorded into the voice chip in segments (SPI mode to copy the voice information of multiple chips.
System software design
Only the combination of software and hardware can better complete the early warning function. The hardware circuit of the system has been designed before. The software part of the function of the early warning system is introduced below.
In the software design process of TMS320LF2407A, assembly instructions are used to set hardware-related registers, and I / O input and output programs are written; and C language is used to write driving safety early warning algorithm programs. The structure of TMS320LF2407A vehicle mountain area safety early warning software is shown in Figure 5. The software design of this system is divided into four modules: main control module, A / D conversion module, I / O module and early warning module. The main control program module controls the operation of the entire software. The A / D module converts the analog signal collected by the sensor into a digital signal; the I / O module controls the TMS320LF2407A and external data input and output; the early warning module obtains the driving safety level value and voice prompt signal. The following mainly introduces the early warning process.
Figure 5 Early warning system software structure diagram
Early warning process
The early warning system is a voice alarm when the car is about to be unsafe when driving on a mountain road. The software structure mainly includes three parts: system initialization subroutine, SPI initialization routine and interrupt service subroutine. The main program is responsible for judging whether it is necessary to broadcast voice information and find the storage address of the voice information. Save it in the APC register of the voice chip. The process of achieving early warning is as follows.
Figure 6 early warning flow chart
The DSP (TMS320LF2407A) A / D interface digitizes the collected information, and then obtains the vehicle driving safety degree value through an early warning algorithm program, and provides an early warning signal to the voice chip ISD1730. The early warning process is shown in Figure 6 (see next page). After the program starts to run, first initialize the DSP control register SCSR, then initialize the A / D control registers ADCTRL, MAXCONV, CHSELSEQ, then set the SPI port parameters, and then configure the interrupt IMR, IFR. After that, the A / D automatic conversion starts to run, and the vehicle operating conditions, road parameters and surrounding environmental conditions obtained by A / D sampling are calculated by the mountain road vehicle driving safety early warning algorithm to calculate the safety level value of the vehicle at that time. Then compare and judge the safety thresholds in the model and execute different procedures according to the different levels of early warning safety. When the security level is low, the DSP executes an early warning subroutine to perform early warning of voice broadcast.
Conclusion
In this paper, through the software and hardware design of the mountain road safety warning system, the final goal is to realize the safe driving of the vehicle on the mountain road, and to remind the driver within a few seconds before the danger will occur, to understand the running state at that time, so as to better Make corresponding remedies. This has great practical significance for reducing road traffic accidents in mountain areas and guaranteeing people's property and personal safety.
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