2013年江西省大学生电子设计竞赛试题C题简易数字万用表任务设计并制作一台支持直流电压、直流电流、电阻测量的数字万用表。要求基本要求测量范围：直流电压0.1V-100V；直流电流10mA-500mA；电阻100Ω-1MΩ。测量精度：±5%。使用按键或者拨码开关进行测量类型选择，并用数码管显示器显示测量数值，发光二极管指示测量类型与单位。发挥部分扩大测量范围：直流电压0.01V-250V，直流电流5mA-1A，电阻10Ω-10MΩ。提高测量精度：±2%。支持电容、电感测量：电容1uF-100uF，精度5%；电感100uH-10mH，精度5%。实现自动量程切换。其他。说明系统采用15V500mADC电源供电。允许采用单片机进行电路设计。不允许采用万用表专用芯片实现电路功能。设计中可使用运放、AD转化芯片、继电器、模拟开关等来实现电路功能。目录1设计方案······························································1.1电路方框图及说明··················································2方案比较选择及硬件模拟设计·······································2.1电压测量电路····················································2.2电流转电压测量电路···············································2.3电容测量电路···················································2.4电阻测量电路···················································2.5比较电路·························································2.6程控电路··························································2.789C52控制及显示模块···········································3系统软件设计·······················································4.数据测量方案及其误差分析···················································4.1电压测试及分析·······················································4.2电流测试及分析·························································4.3电容测试及分析······················································4.4电阻测试及分析·····················································5结论·································································参考文献··································································附录·····································································1方案设计1.1电路方框图及说明系统分四大部分，及测量电路，通道选择，控制电路和显示电路，如下图所示。AT89C51根据所选通道,取得模拟信号,然后进行模数转换进行比较判断是否转换量程，通过比较后确定了在哪个量程测量精度高则通过1602显示测量结果。按键换档位测量电容RC震荡RC震荡测量电阻多通道选择开关量程切换TLC2543数据采集、控制、档位切换STC89C52测量值显示电路二极管显示档位选择测量电压量程自动切换电路测量电流电流转电压测量电路控制电路数据通道选择1.2方案比较与选择1.电容、电阻测量电路方案选择：方案①：.振荡法这种方法的思想是将较难测量的物理量转变成精度较高且较容易测量的物理量。基于此思路，我们把电子元件的集中参数R、C转换成频率信号f，然后