Abstract:

With the continuous upgrading of auto manufacturing technology,the new automobile engine is very compact in structure,which makes it difficult to directly approach the automobile engine ignition coil part,so the traditional vehicle speed detection through ignition pulse fails to meet the present measurement requirements.By theoretical analysis,the speed of automobile generator and engine are correlated,the output of the generator are three phase voltages,through a bridge rectifier connected to the vehicle battery,and getting the terminal voltage signal from the car cigarette lighter is a simple operation.Multistage band-pass filter circuit is used to realize weak electrical signal noise filtering and voltage amplification,after which the fast discrete Fourier transform is employed to realize real time signal spectral analysis to obtain the frequency related to the car speed for calculating the speed of automobile engine.

Key words: car engine speed measurement;FFT;active filter;harmonic analysis