Design And Implementation Of Overland Doppler Log Based On MCU

Now, in different of vehicle integrated navigation systems, SINS/OD and DR systemsare all need Odometer to measure vehicle speed relative to ground, The velocity precisiondirectly impacts on the accuracy of vehicle navigation system. However, when vehicle skidsor the radius of vehicle’s wheel changes, Odometer calibration factor will be changed, so itsprecision of measuring velocity is unstable. In high precision occasions, Odometer can’t meetthe requirement.In order to overcome the shortcoming of Odometer, this paper borrows insights fromDoppler log technology and designs a high-precision and low-cost instrument—OverlandDoppler log that can measure the vehicle’s speed. It is based on Doppler Effect, it usingpiezoelectric transducer for emitting ultrasonic to ground obliquely and can calculate vehiclespeed by measuring the Doppler frequency shift between the transmission signal and thereceived signal that reflect back from the ground.This paper studies the design and implementation of Overland Doppler log andcompletes the design of system’s hardware and software, system testing and functionalverification. It uses K60DN512microprocessor chip as the core. K60DN512’s internal PWMgenerates40KHz square wave, and then IR2111amplifies the square wave using Class Dpower amplifier to load to impedance matching network. Lastly piezoelectric transducer isdriven to emit ultrasonic. The echo signal the transducer receives is amplified byprogrammable amplifier. Then signal amplified will go through a band-pass filter constitutedby OPA4132. The signal from band-pass filter will be sampled by K60DN512’s internal ADC.For the processing of the echo signal, this paper studied implementation method of thezero-crossing algorithm、software PLL and complex covariance for the estimation of thefrequency. Analyses which use MATLAB simulation tool of computation and precision aregiven. The results show that: in regard to the other two algorithms, the complex covariancehas a small amount of calculation, high frequency measurement accuracy, and more suitablefor hardware implementation. Taking into account implementability of hardware, authorchose the complex covariance to estimate the frequency of the echo signal.Lastly, the debugging and simulation to Overland Doppler log is given. The main signalwaveform is tested in the lab, the results show that the major waveform meets the designrequirement, each hardware subsystem is stable and reliable. Because of piezoelectrictransducer’s bad performance, the velocity precision dosen’t meet predetermined requirements.The real reasons: transducer’ beam is too wide, different angles of acoustic line which reflect from ground have different Doppler frequency shift, and then causes Doppler frequency shiftextension. The result that the frequency spectrum of the received signal is wider than thetransmit signal spectrum, and eventually cause the larger the speed error. To ensure transducerperformance, we should be use transducers the professional manufacturer made which beamwidth is very small. For testing the level of accuracy of the complex covariance algorithm,the author use MATLAB to simulate the algorithm for the estimation of the frequency, theresults show that algorithm’s accuracy level meets the requirements of vehicle’s velocityprecision, the design proposal of Overland Doppler log is feasible.