Design conception of braking distance tester for t

2022-08-10
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Design conception of automobile braking distance tester

Abstract: through the analysis of automobile braking and parking process, Based on the principle of microwave radar ranging, an automatic measurement and display instrument is designed, which uses the Doppler radar sensor to scan the relatively moving ground, and the frequency shift (proportional to the vehicle speed) signal obtained is processed by the single chip microcomputer in time, and then controls the dot matrix LCD to display the vehicle braking and parking distance. The design cost and market demand are briefly analyzed

key words: braking distance, radar, design

1. Analysis of car braking and parking process

traffic accidents are sudden, which makes drivers unprepared. Now let's analyze the whole process of braking and parking. Analysis as shown in the figure:

t1=t1 '+t1' is the driver's reaction time, which is generally 0.6s~1.0s

t2=t2 '+t2' -- the action time and hysteresis time of the brake are collectively referred to as the hysteresis time. Generally, 6. The main matters for soliciting public opinions are 0.2~0.9s

t3 is the braking effective time, and the deceleration of the car within this time is basically unchanged (ABS has a wave 'straight line' trend), That is, the time required for braking to stop at the maximum braking intensity. The braking and parking process can be roughly divided into two processes: 1. The first process is from sending the braking signal to the driver making the braking action (touching the brake pedal with his foot); 2. The second process is from the driver making braking action (touching the brake pedal with his foot) to the vehicle stopping

2. Design of brake stopping distance tester

2.1 system composition and working principle

the function of this system is coordinated by hardware and software. The hardware part mainly completes the collection, transformation, processing of various sensor signals, display of various information, etc

the software mainly completes the signal processing and control functions. Its working principle is that the velocity sensor adopts Doppler velocity radar. When the car is driving, the Doppler radar antenna continuously transmits electromagnetic waves to the ground at a certain frequency and receives the reflected electromagnetic waves at the same time. By measuring the difference between the emission and reception of the car radar, the car speed and displacement can be calculated in real time and accurately. When the tester sends the detection signal, the system starts timing. ATmega16 AVR MCU queries the output signal of Doppler radar sensor and processes the data of each time period; Then the input signal is processed and output through the display module lcm12232f. The output signal parameters include: driver's reaction time, reaction distance, braking time, braking distance, electromagnetic interference intensity, etc. So as to test the braking performance of the driver and the car. At the same time, it can also output various prompt alarm signals. The hardware structure of the system is shown in the figure

2. 2 hardware composition

the system hardware mainly includes the following modules: ATmega16 AVR single chip microcomputer main control module, power supply module, sensor detection module, ADC analog/digital conversion module (using single chip microcomputer on-chip ad to display the results with images and numbers), lcm12232f display module, etc. ATmega16 AVR mainly completes the control of peripheral hardware and some operation functions. The power module supplies power to the whole instrument system, the sensor completes the signal sampling function, ADC completes the function of converting analog signals into digital signals, and lcm12232f display module completes the display function of characters and numbers

2.2.1 the pin of the main control module

atmega16

the system adopts the 8-bit AVR single chip microcomputer ATmega16 produced by ATMEL company, which is a programmable microcontroller with 16K byte flash

2.2.2 Doppler microwave ranging radar sensor

comprehensive needs us to select 4803 Doppler microwave ranging radar sensor, Its main parameters are as follows:

dc8v power access port

microwave cavity oscillator frequency is 10.525g

30MW frequency generator receiver (size 40x60x62)

radar antenna receiver box (appearance 85x69x21mm)

bismuth output interface adjacent to lead in the periodic table for TTL data (with data extension cable)

2.2.3 dot matrix liquid crystal display module

microcomputer controlled electronic universal experimental machine is your better choice

here we use lcm12232f, which is a graphic dot matrix liquid crystal display with 8192 16*16 dot Chinese character libraries and 128 16*8 dot ASCII character sets. As shown in the following figure:

it is mainly composed of row drive/column drive and 128 × 32 full dot matrix LCD. Graphic display can be completed, and 7.5 can also be displayed × 2 (16 × 16 dot matrix) Chinese characters The interface with external CPU is controlled in parallel or serial mode

2.2.4 electromagnetic detection sensor

select key/z 20s magnetoresistive sensor

open circuit sensitivity 4.7 (mv/v)/(ka/m)

output hysteresis voltage

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