In recent years, in the daily training process of armored vehicles, vicious accidents have occurred, which has caused great losses to the lives and equipment safety of the troops. Armored vehicles usually use closed-end driving while driving, the driver's line of sight is affected, and the training of the troops is often in the hilly area, the road conditions are very bad, especially the northern troops, often accompanied by a large amount of dust during training, which greatly increases the number of The probability of occurrence of a vehicle accident. The causes of collisions of armored vehicles are very complicated. There are factors of armored vehicles themselves, factors of human factors, environmental factors such as roads and meteorology. In short, people, vehicles and the environment are the three major factors affecting the safety performance of vehicles. The three constitute a system engineering that restricts each other.
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In order to solve the safety problem of armored vehicles training, this paper proposes to develop an armored vehicle anti-collision warning system that can obtain vehicle position information in real time and promptly remind the driver or the system to take measures to avoid dangerous situations. The research and development of this system is extremely Great practical significance and broad application prospects.
Introduction to common vehicle distance detection technology
At present, distance sensors are mainly divided into three categories: acoustics - ultrasonic; optical - passive infrared, laser radar and video imaging systems; electromagnetic - continuous wave radar / single pulse radar and capacitive sensors. Every distance detection technology has its own application.
(1) Ultrasonic sensor
Ultrasonic waves are sound waves whose frequency is above 20 kHz and which are not felt by the human ear. Compared with audible sound, it is characterized by high frequency, short wavelength, good beamability, penetration and directionality in propagation. Ultrasonic distance sensors generally use separate transmitters and receivers. The transmitters are excited by high frequency signals (40KHz~80KHz). By measuring the time interval between the transmission of an ultrasonic pulse and the receipt of the reflected signal, the distance of the measured object can be simply estimated.
Its main advantages are lower cost and smaller size; the main disadvantage is that some targets (such as soil and vegetation) have weak reflection signals and cannot be detected. Another disadvantage is that the propagation time of sound waves in the air varies with temperature. Therefore, when the ultrasonic sensor is used in a temperature range, temperature compensation must be performed. Therefore, ultrasonic sensors are generally used for short distance measurements, and the optimum distance is 4 meters to 5 meters.
(2) Passive infrared sensor
Passive infrared sensors are based on measuring the thermal energy emitted by objects near the sensor to achieve ranging. Like the ultrasonic distance sensor, the main advantage of the passive infrared sensor is its low cost and small size. The main disadvantage is that the response time is too long, so that the driver's early warning is often not enough to avoid collision, which limits its collision alarm in the vehicle. Application in the system.
(3) Lidar sensor
Since the beam is generally concentrated, the lidar is mainly used for the measurement of a wide range of linear distances. Lidar has a large range, strong directionality and fast response time, but it is costly and vulnerable to external environment (such as low visibility and mud on the sensor surface). At the same time, the laser energy must be within the safety level of the human eye.
(4) Continuous wave radar sensor
CW radars use frequency-modulated high-frequency electromagnetic carriers (typically microwave frequencies or higher, usually zigzag signals). Comparing the reflected signal with the transmitted signal, a frequency difference proportional to the measured distance can be obtained. The relative velocity of the measured object can also be determined by the Doppler deflection of the return signal.
The outstanding advantage of CW radar is its ability to "see" objects through dirt and spatter; and both narrow and wide beams can be used, making it possible to tailor the beam width to a particular application. The main disadvantage is that the electromagnetic devices in the microwave and millimeter wave bands are relatively expensive. In addition, electronically scanning a relatively narrow beam with a large detection range results in a larger measurement range and beamwidth, but the complexity and cost increase.
Basic functions and working principle of anti-collision warning system
According to the need for armored vehicles to prevent collisions in field conditions, the system should have the following functions:
(1) Position and display nearby vehicles. It should be possible to locate the nearby vehicle and display it on the display.
(2) Alarm when the distance between the two vehicles is less than the safe distance. The distance between the two workshops should be accurately measured. When the distance between the two vehicles is less than the safety distance (5m), an alarm is issued to alert the driver.
The working principle of the system: The system uses the GPS system to locate the vehicle, receives the surrounding vehicle position through the wireless module and sends the vehicle position outward. Display the surrounding vehicles on the display and calculate the distance between the two vehicles. When the distance between the two vehicles is less than 15m, the distance sensor is used for accurate distance measurement, and when the distance is less than 5m, an alarm is issued. Compared with the performance of each sensor in the common vehicle distance detection technology, since the distance sensor distance measurement does not need to be too far, combined with cost and volume considerations, the ultrasonic sensor is selected as the close range finder in the system.
An ultrasonic sensor is a device that converts other forms of energy into ultrasonic energy of the desired frequency or other forms of energy that converts ultrasonic energy into the same frequency.
Ultrasonic ranging can be divided into two types: resonant and pulsed. Due to the application requirements, pulse reflection is used here, that is, the reflection characteristics of the ultrasound are utilized. The principle of ultrasonic ranging is to transmit ultrasonic waves in a certain direction through an ultrasonic transmitting sensor, and start timing at the same time as the transmitting time. The ultrasonic waves propagate in the air, and immediately return to the obstacle when the obstacle is encountered on the way, and the ultrasonic receiver stops counting when receiving the reflected wave. . According to the time t recorded by the timer, the distance (S) of the emission point from the obstacle can be calculated, that is, S=C×t/2, where C is the ultrasonic sound speed, and since the ultrasonic wave is also the sound wave, C is the speed of sound. .
Empirical formula for sound velocity and field temperature: C = 331.5 + 0.607T. As long as the time difference t of the ultrasonic transmitting and receiving echoes and the field temperature T are measured, the distance from the transmitting point to the obstacle can be accurately calculated.
It can be seen that the main parts of the ultrasonic ranging system are:
(1) a pulse generator (transmitting circuit) for supplying electric energy;
(2) a switch portion that isolates the receiving and transmitting;
(3) converting the electrical energy into acoustic energy and transmitting the acoustic energy to the transmitting sensor in the medium;
(4) receiving a reflected acoustic energy (echo) and a receiving sensor that converts the acoustic energy into an electrical signal;
(5) The receiving amplifier can amplify the weak echo to a certain amplitude and cause the echo to excite the recording device;
(6) A recording/control device that typically controls the power delivered to the sensor and controls the time at which the acoustic energy pulse is transmitted to record the echo, stores the required data, and converts the time interval into a distance.
In the ultrasonic measurement system, the frequency acquisition is too low, and the external noise is more disturbed; the frequency is too high, and the attenuation is large in the process of propagation. Therefore, in ultrasonic measurement, ultrasonic waves of 40 kHz are often used. At present, the distance measured by ultrasonic waves is generally several meters to several tens of meters. Ultrasonic transmitting and receiving devices have high anti-interference performance due to their inherent frequency characteristics.
The distance measurement system usually uses a pulse pressure wave with a frequency range of 25 kHz to 300 kHz. The transmitting and receiving sensors sometimes share one and sometimes separate. The transmitting circuit is generally composed of two parts: an oscillation and a power amplifier, and is responsible for outputting a high-voltage pulse train having a certain width to the sensor, and converting the sensor into sound energy to be emitted; the receiving amplifier is used for amplifying the echo signal for recording, and in order to enable it to receive A short pulse signal with a certain frequency bandwidth, the receiving amplifier should have sufficient frequency bandwidth; the receiving/transmitting isolation enables the receiving device to avoid a strong transmitting signal; the recording/control portion activates or deactivates the transmitting circuit and records the instantaneous and received transmission. Instantaneously convert the time difference into a distance reading and display or record it.
Overall structure of the system
The main purpose of the design of the system is to locate and display the location of nearby vehicles, measure the distance between the vehicles, and issue an alarm when it is dangerous.
According to the actual functional requirements, the overall design of the system is divided into two parts: the detection system and the data processing system. The basic principle is shown in Figure 1. The detection system mainly comprises a GPS module, an ultrasonic ranging module, a wireless module, a power module, a main control circuit and a communication interface; the data processing system mainly comprises a display module, an alarm module, a power module and a main control circuit.
Sensor, GPS and wireless module selection
(1) Selection of ultrasonic sensors
Ultrasonic sensor adopts Sens600 series intelligent ultrasonic sensor of SensComp Company of USA. Sens600 is an enhanced electrostatic sensor series based on ultra-sensitive distance measuring module 6500. It integrates transmission and reception. The new voltage control circuit enables the sensor to work at 6V~24V DC. Under the power supply, the measuring range is 0.15m~10.7m, which can be externally triggered or internally triggered. The package is small and the terminal pins are convenient to connect. Since the ultrasonic sensor outputs a high level when receiving the echo signal, it is necessary to connect the inverter to the external interrupt port of the MCU at the output of the echo for immediate response. In addition, a flared sleeve design is added to the open end face of the ultrasonic sensor to limit and reduce the large transmitted wave and the received wave from the center of the emission axis, which enhances the anti-interference ability to a certain extent.
(2) Selection of temperature sensor
The existing temperature sensors are mainly divided into two types, namely digital temperature sensors and analog temperature sensors.
Digital temperature sensors measure temperature by directly converting temperature values ​​into digital value outputs. The digital temperature sensor has the following advantages: 1 high measurement accuracy and resolution, large measurement range; 2 strong anti-interference ability and good stability; 3 signal easy to process, transmit and automatically control; 4 convenient for dynamic and multi-channel measurement, Intuitive reading; 5 easy to install, easy to maintain, high reliability.
In combination with various factors, this article selects the single-line digital temperature sensor DS18B20 from Dallas Semiconductor.
(3) GPS selection
The Smart Antenna Module includes a complete GPS receiver with built-in antenna for fast system integration, giving it a completely independent GPS function. Based on this fully designed GPS subsystem, integration requires minimal development time and minimum development. Cost and minimum development risk. The choice of GPS smart antenna module is mainly considered: 1 characteristics (such as energy-saving mode and support for SBAS); 2 ease of use (especially easy to configure); 3 quantitative indicators (measured parameters), such as accuracy, startup performance, tracking Sensitivity and power consumption; 4 qualitative indicators, including predictable positioning results obtained from field tests.
Considering various factors, this article uses Starlight's ZG-P1121U module.
(4) Choice of wireless module
The selection of the wireless module mainly considers the following factors: 1 transmission distance, the transmission distance of the wireless module must meet the needs of the armored vehicle field conditions; 2 anti-interference, the ability to resist sudden interference and random interference; 3 operability, There must be a programmable channel to meet the user's multiple communication combinations; 4 economical, cost-effective; 5 safe and convenient, installation, maintenance, replacement should be convenient and fast, small size, light weight and so on.
Considering various factors, this paper selects the TDX-2000 wireless data transmission module launched by Shenzhen Taidaxin Communication Technology Co., Ltd.
Detection system design
The detection system refers to the part of the system responsible for data detection and transmission. The basic task is to receive commands from the data processing system, use GPS and ultrasonic sensors to locate and measure, receive the surrounding vehicle position through the wireless module and send the vehicle position outward. The detected data is transmitted to the data processing system via the communication interface. The structure of the detection system is shown in Figure 1.
Figure 1 Overall structure of the system
Circuit design of the detection system
The circuit design of the detection system mainly includes the design of the ultrasonic module circuit and the design of the communication interface circuit. Both the GPS module and the wireless module are connected to the single-chip microcomputer for data transmission through RS-232 serial communication.
Ultrasonic ranging module circuit design
(1) Ultrasonic transmitting circuit design
The ultrasonic transmitting circuit is shown in Figure 2.
Figure 2 Ultrasonic transmitting circuit diagram
(2) Ultrasonic receiving circuit design
The ultrasonic receiving circuit is shown in Figure 3.
Figure 3 Ultrasonic receiving circuit diagram 
Temperature measurement circuit design
The temperature is measured by the digital temperature sensor DS18B20, and the collected temperature data is transmitted to the main chip through the P54 pin of the main chip MSP430F149.
The DS18B20 can be connected in two ways: one using a parasitic power supply and the other using an external power supply. When using the parasitic power mode, a strong pull-up is provided to the I/O lines when performing temperature conversion or copying to E2 memory operation. This can be achieved by pulling the I/O line directly to the power supply with a MOSFET. After issuing any protocol involving copying to E2 memory or initiating a temperature conversion, the I/O line must be converted to a strong pull-up within a maximum of 10 μs. When using parasitic power mode, the VDD pin must be grounded.
When using an external power supply, the pin VDD is connected to V+5. This has the advantage that the pull-up is not required on the I/O line, and the bus controller does not always remain high during temperature conversion. This allows other data transactions on the single-wire bus during the conversion. When an external power supply is applied, the GND pin cannot be left floating.
According to the needs and actual conditions of the system, the parasitic power supply is used here, and the P54 pin of the main chip is used for the data input/output pin of the DS18B20. The specific circuit is shown in Figure 4.
Figure 4 temperature measurement circuit diagram
Communication interface circuit design
The communication interface is responsible for the data exchange between the GPS module and the wireless module and the main chip, and the data exchange between the detection system and the data processing system.
Serial communication requires only a small number of ports to achieve interoperability between the microcontroller and peripheral devices, with unparalleled advantages. There are two ways to communicate serially: asynchronous mode and synchronous mode. The MSP430 series has a USART module for serial communication. In this design, the USART0 module of the MSP430F149 communicates with peripheral serial devices via the RS-232 serial port.
This system uses a dedicated level conversion chip MAX3232 to achieve communication (see Figure 5). The MAX3232 chip is a level-shifting chip produced by MAXIM. It consists of two receiver and driver IC chips. It has a power converter inside, which can convert the input +5V voltage to the -10V required for the RS-232 output level. +10V voltage.
Figure 5 Communication interface circuit schematic
Data processing system design
The data processing system is responsible for displaying and calculating the data collected by the detection system. The specific tasks are: 1 controlling the working state of the data acquisition system; 2 receiving and displaying the position information collected to the surrounding vehicles; 3 when the distance between the two vehicles is less than the safety distance Alert.
The data processing system is mainly composed of main control circuit, keyboard, liquid crystal display, buzzer alarm circuit and communication interface. The structure of the system is shown in Figure 1.
Liquid crystal display circuit design
The principle of liquid crystal display is to use the physical characteristics of liquid crystal to control the display area by voltage, and display when there is electricity, so that the figure can be displayed. The liquid crystal display has the characteristics of thin thickness, direct driving for large-scale integrated circuits, and easy realization of full-color display, and has been widely used in many fields such as portable computers, digital cameras, and PDA mobile communication tools. There are many types of liquid crystal display classification methods, which can be divided into segment type, character type, dot matrix type and the like according to the display manner.
The dot matrix form liquid crystal is composed of M×N display units. It is assumed that the LCD display has 64 lines, each row has 128 columns, and each 8 columns corresponds to 1 byte of 8 bits, that is, each line consists of 16 bytes, a total of 16× 8 = 128 points, 64 × 16 display units on the screen correspond to 1024 bytes of the display RAM area, and the content of each byte corresponds to the light and dark of the corresponding position on the display screen.
According to the needs and actual conditions of the system, the dot matrix display liquid crystal display is used here, and the P30 pin of the main chip is used for the data input/output pin. The specific circuit is shown in Figure 6.
Figure 6 LCD circuit diagram
Alarm circuit design
When there is a situation in the armored vehicle driving, the driver needs to get an audible alarm prompt, but considering that the audible alarm time is short, the audible prompt may be too late, so the system alarm mode is designed as an audible alarm and a light flashing warning. The illuminating alarm module is realized by a light-emitting 8-bit diode controlled by a single chip microcomputer. The buzzer emits a signal of audible alarm. The design of the alarm unit in this paper adopts the combination of sound and light according to different danger levels, which is more in line with the requirements of military training.
The audible alarm uses a buzzer to output pulse control through the I/O port, changing the frequency and duration of the pulse to perform different types of prompts or alarms. In order to improve the driving ability and let the buzzer produce a certain intensity of sound, a symmetrical transistor drive is used, and its circuit is as shown in FIG.
Figure 7 buzzer alarm circuit schematic
System software design
The system software design includes the software design of the detection system and the software design of the data processing system.
(1) The software of the detection system mainly has the following tasks:
1 complete the initialization of hardware systems such as special function registers and I/O ports;
2 with GPS module, ultrasonic module, temperature sensor and wireless module initialization and inspection functions;
3 has a temperature digital signal receiving and storing function for the temperature sensor;
4 Complete the initialization function of the communication interface to realize data transmission with the GPS module, the wireless module and the data processing system;
5 has the function of power detection and maintaining low power consumption;
6 has a data filtering function, eliminating the data with large errors collected.
(2) The main tasks of the data processing system software are:
1 complete the initialization of hardware systems such as special function registers and I/O ports;
2 Complete the display to display the collected data display;
3 complete the alarm function;
4 complete the communication module design.
Conclusion
In view of the safety problems existing in the training process of armored vehicles, this paper proposes to design an armored vehicle anti-collision warning system. The system can obtain the vehicle position information in real time, promptly remind the driver or the system to take measures to avoid dangerous situations, the system principle is feasible, the circuit is reliable, and the application prospect is broad.
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