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摘 要
随着科技的迅速发展，单片机的应用也越来越广泛，并带动传统控制检测技术不断更新。现在的车速表大多是电子式的，用LED数码管或LCD即时显示，显示更加直观。电子式车速表采用接触车速传感器代替软轴传动,可使车速表的安装位置不受距离限制，进一步有效地克服了机械式车速表中的诸多不足。
本次设计给出了以AT89C51为核心，利用单片机的运算和控制功能，并采用系统化LED显示模块实时显示所测速度的设计方案，以及串口数据存储电路和系统软件。
该方案由于使用了数码管显示模块和E2PROM，以及高效快速算法，因而可在节约系统资源和简化程序设计的基础上保证测量精度和系统实时性。其中信号预处理电路包含信号放大、波形变换和波形整形：信号预处理电路中的放大器用于对待测信号进行放大,以降低对待测信号的幅度要求；波形变换和波形整形电路则用来将放大的信号转换成可与单片机接口的TTL 信号。通过单片机的设置可使INT0 引脚能够对内部定时器T0 的工作进行控制,这样能精确地测出加到INT0 引脚的正脉冲宽度(即测出脉冲信号的期) 。速度显示部分采用数码显示, 所得的数据采用I
本方案实现了电动车速度即时显示，并可通过控制两个按键显示速度或里程，同时加入了超速语音报警功能，使之更加人性化。
关键词：单片机；霍尔传感器；数码显示；语音报警；DC/DC变换器
Abstract
With the rapid development of technology, more and more widespread application of microcomputer, and promote the traditional control detection technology constantly updated. Most of the current electronic speedometer, and with the LED digital tube or LCD display real-time, display more intuitive. Electronic speedometer flexible shaft using the contact speed sensor instead of driving, speed tables can be installed without distance limitations, and further to effectively overcome the mechanical disadvantages of speed in the table.
The AT89C51 is designed to give the core of computing and the use of microcomputer control, and adopting a systematic LED display module shows the measured real-time speed design, and the serial data storage circuits and system software.
The program due to the use of the digital display module and E2PROM, and efficient fast algorithm, thus saving resources and simplifying programming system based on the system to ensure accuracy and real-time. Signal pre-processing circuit which includes signal amplification, wave conversion and waveform shaping: signal pre-processing circuit in the amplifier for the amplified signal could be to reduce the requirements on signal amplitude; wave transformation and wave-shaping circuitry is used to enlarge the signal converted into TTL signals with the microcontroller interface. Set by MCU enables INT0 pin to the work of the internal timer T0 control, so to accurately measure the INT0 pin is added to the pulse width (ie measured pulse signal period). Speed display part of a digital display, the data collected using I
The program achieved the speed of real-time electric vehicle revealed two buttons can be displayed by controlling the speed or mileage, while adding a speed voice alarm function, make it more humane.
Key words: microcomputer； Hall sensor； digital display；voice alarm； DC / DC converter