Development Of A Portable Speed Measuring Instr Ument For Automotive Engine

With the development of the automobile industry, automobile performance has become more and more attention by people at present. The engine revolving speed, directly reflects automotive engine’s performance, is an important indicator of automobile power. Revolving speed measurement technology has being the basis of the engine measurement technology. A variety of measurement systems have formed under the previous continuous efforts, but there are also a few disadvantages in these methods in practical application. For example, most of the methods would need to install the measuring sensor on the bent axle. These methods direct and effective but bring inconvenience to the engine manufacture and maintenance.This thesis develop a portable engine speed meter according to the connection between the generator speed with engine speed of the car and the connection between generator power system and vehicle electronic systems to solve the inconvenience. The meter is characterized by getting the original signal of the car from cigarette lighter, then extracting the coupling AC signal of the generator through filter circuit, and then analyzing the signal to gain the engine speed indirectly. Therefore, the meter can not only keep the original structure of the car, but also measure the engine speed in real time exactly and quickly without any sensor on the engine.The meter is based on TMS320F2812which is one of the digital signal processors. Signal preprocessing circuit will limit the input analog signal amplitude between0and3.3V, in order to satisfy the requirement of ADC which is built-in the TMS320F2812. After sampling, the input analog voltage signal is converted into digital signal, and then do the digital signal FFT arithmetic, the frequency domain discrete spectrum, and scan from the spectrum to pick out the input signal fundamental frequency, according to the relationship of the frequency and engine speed, the engine speed are obtained. In addition, the meter adopts the12864LCD to display datum,4x4keyboards to input user instruction, and designs the detailed function menu, applicable to different ways of signal acquisition, has the good human-computer interaction.The meter adopts external usb interface to storage test datum, it is easy to copy these datum to PC for viewing and analyzing.