基于CAV424的粮食含水率测量系统的设计
摘要
粮食含水率作为评价粮食品质的一项重要指标，如果其值过高，容易引起粮食变质，重量加重，增加运费；反之，其值过低，则容易损坏有机物质，粮食品质下降。粮食含水率检测结果的准确性、快速性对粮食的安全存储、运输等有十分重要的作用。因而设计一种粮食含水率测量系统具有很重要的现实意义。
本文在分析粮食的介电特性的基础上，提出了基于脉宽测量的电阻比值法的测量方法，详细介绍了它的测试原理、硬件结构和软件流程。该测定仪具有测量精度高、低功耗、便于携带、操作方便、人机界面友好等特点。硬件部分主要由电阻式水分取样电路、信号调理电路、LCD显示电路、键盘扫描电路、电机驱动电路、RS232接口电路等。、要求该系统能够稳定、准确、快速地测量出粮食含水率；并且成本低、测量范围较大（可选定10%RH-30%RH）；其中，对于电阻式水分取样电路是基于555实现的。该设计是基于CAV424完成的， 该微控制器是针对工业应用方案而设计的，它还具有一个电池备用的休眠模块，从而有效的使CAV424芯片在未被激活的时候进入低功耗状态，这为用户提供了灵活性，能够适应各种精确的需求。
关键词：水分测定；电阻比值法；CAV424；555
Abstract
Grain water content is an important index to evaluate grain quality. If its value is too high, it can easily cause grain deterioration, weight increase and increase freight rate. On the contrary, its low value is easy to damage organic matter and grain quality. The accuracy and rapidity of the results of grain moisture content play a very important role in the safe storage and transportation of grain. Therefore, it is of great practical significance to design a grain moisture content measuring system.
Based on the analysis of the dielectric properties of grain, a measurement method based on the resistance ratio method based on pulse width measurement is proposed, and its testing principle, hardware structure and software flow are introduced in detail. The instrument has the characteristics of high accuracy, low power consumption, portability, convenient operation, friendly man-machine interface and so on. The hardware part mainly consists of resistance water sampling circuit, signal conditioning circuit, LCD display circuit, keyboard scanning circuit, motor drive circuit, RS232 interface circuit and so on. It is required that the system can measure the moisture content of grain steadily, accurately and quickly, and the cost is low and the range of measurement is large (10%RH-30%RH); among them, the resistance water sampling circuit is based on 555. The design is based on CAV424. The microcontroller is designed for industrial applications. It also has a battery standby dormancy module that effectively enables the CAV424 chip to enter a low power state when it is not activated, which provides the user with flexibility and can adapt to a variety of precise requirements.
Key words: moisture measurement; resistance ratio method; CAV424; 555;
摘要 1
Abstract 2
1 绪 论 3
1.1 研究背景及意义 4
1.2 国内外研究现状 5
1.3 水分检测技术的发展趋势 6
1.4 本文研究内容 7
2系统基础和概述 7
2.1方案设计与论证 8
2.2系统控制器介绍 8
2.3 555集成定时器的介绍 10
2.4 液晶显示模块的介绍 11
2.5 EEPROM存储器的介绍 12
2.6 电机驱动芯片的介绍 14
3 系统硬件设计 16
3.1系统基本组成 16
3.2 电机驱动模块 17
3.3 EEPROM存储器模块 17
3.4 信号调理电路模块 18
3.5 显示模块 19
3.6 键盘模块 20
3.7 单片机模块 21
3.8 电源模块 22
结论 23
参考文献 24
附录（原理图） 25
参考文献
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