The Reasearch Of The Car Speed System

This topic is based on the Social Development Fund Project in Tianjin (09ZCGYSF00300)"Research of Speed Secure Real-time monitoring system for measuring traceable calibration standards". Following with the developing of China’s economy and society,the growing of crowds,traffic,logistics,road traffic accidents remains high,the control of traffic accident,Traffic monitoring real-time monitoring system has become an important part, caused traffic jams and the most important reason of traffic accidents is speeding. Currently, the endless use on the road speed measuring device and most belong to the fixtures, it is necessary to develop a mobile tacho, not only to facilitate the measurement of vehicle speed, but also facilitates the calibration of the other vehicle speed measuring device.Therefore,This paper’s job is as follows:1、Existing sense coil tachometer, radar guns, video speed, GPS speed measurement, laser speed, five mainstream tacho analysis, compare their advantages and disadvantages. Based on a comprehensive analysis of the Fifth mainstream tacho focuses on the principle of laser speed, and analysis of the laser speed three typical methods, and compare their advantages and disadvantages, and the final choice for automotive tachometer and proposed the overall framework of this paper to study automotive laser velocimetry system and the working process of the system.2、Auto laser velocimetry system hardware is divided into a laser emitting portion, and the laser receiving portion, the precision time interval measuring section and the data processing and the display portion.Laser emitting portion:the design principle of the laser emission is divided into pulse width shaping, driver amplifier, the energy storage and the laser emitting portion. Selection SPL_L90as the front-end laser light emitting diode, the use of FPGA phase-locked loop (PLL) multiplier of the reference pulse, generating a very narrow pulse signal, through the driver chip MIC4452extremely narrow pulse signal is converted to a large-current signal driving SPL_L90thereby the issue of a pulsed laser.Laser-receiving portion:the structure of the laser velocimetry system receiving module, select AD500-9type avalanche photodiode as the optical receiving device, and provides the AD500-9avalanche diode to a high pressure feedback power supply circuit, the electrical signal with Ua733A zoom amplified noise signal, is also in the process of amplification, MAX913high-speed comparator is its pulse shaping.3、Automotive laser velocimetry system timing design measurement modules and data processing moduleHigh-precision time interval measurement part:high-precision time measurement method, including the Law of the direct measurement of the number of interval extension method, time -amplitude conversion method, the cursor method, and describes a high-precision time measurement of basic devices into environmental Quartus Ⅱ software ultimately FPGA logic devices, pulse counting method to design a high-precision time measurement module, the measurement accuracy can be achieved Ins. Measuring range up to1024ns.Data processing and display parts:in the FPGA to achieve high precision time interval acquisition of the laser transmitter and receiver interval to the microcontroller via the SPI bus interface transfer MCS-51microcontroller MCS-51completed its data processing, and the speed display in the LCD1602.Through this design, it is possible to detect the vehicle speed range (20to180) km/h speed error:1%.