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1、人体体重秤设计课程设计北京信息科技大学仪器科学与光电工程学院测控0901林杰20090107442012/6/20本文介绍以AD620、LM741、LM339为核心的智能人体电子秤的设计,详述该系统硬件的设计方法。该系统集称重、显示、报警于一体,功能齐全,实用性强，充分利用了电路、模电、测控电路、信号处理等课堂上学到的知识。-19-目录一、系统设计及工作原理·························2二、模块电路设计·····························41、称重传感器模块···
2、························52、滤波及放大电路··························32-1仪用放大器的原理·························42-2四种放大器电路论证·····················62-3AD620主要性能指证·······································82-4调零电路······················································92-5放大部分电
3、路·················································103、报警电路···························································113-1LM339简介-19-··················································113-2LM339制作单限比较器····································113-3LM339制作双限比较器···
4、·································123-4体重秤中使用的电路·······································133-5集电极开路输出原理·····································144、显示模块···························································16三、完整电路图···········································
5、················17四、数据测量及处理·····················································18五、感想和总结··························································19数字电子秤设计测控0901林杰2009010744合作者：杨雪姣-19-【摘要】本文介绍以AD620、LM741、LM339为核心的智能人体电子秤的设计,详述该系统硬件的设计方法。该系统集称重、显示、报警于一体,功
6、能齐全,实用性强，充分利用了电路、模电、测控电路、信号处理等课堂上学到的知识。关键词：AD620；传感器；液晶显示一、系统设计及工作原理本系统主要由称重传感器模块、滤波放大电路模块、报警电路模块、LCD显示模块等部分组成。人体的体重信息由称重传感器转换成电信号,并通过测量电路进行滤波放大,通过显示电路进行显示,如体重超出设定范围系统还会报警。系统结构框图如下图所示。二、模块电路设计1、称重传感器模块-19-称重传感器是影响电子秤测量精度的关键部件。选用适当传感器,用来感知被测量,当物体放在秤盘上时,压力传给
7、传感器,该传感器发生形变,从而使阻抗发生变化,电桥失去平衡,传感器输出一个变化的模拟信号。如图所示，4个电位器式的传感器显示了称重传感器的大体构造。输出电压大约在0-1.5mv左右。已知传感器输出线性，我们所需要做的就是把它进行放大滤波，最终显示出来即可。2、滤波及放大电路目前的电子称重装置大都使用电阻应变桥式传感器,其核心是由电阻应变计(应变片)构成的电桥电路,这类传感器具有成本低、精度高且温度稳定性好的特点。但其检测原理决定该类传感器输出电压低,要经过差分放大电路放大数百倍才能用于后续的电路。2-1仪用
8、放大器的原理-19-一般说来，传感器输出的电压值都非常小，基本上都是毫伏级甚至微伏级。在设计高精度电子秤时，需要外部放大电路来获得足够的增益。因此，我们打算仪用放大器来进行放大，目前，仪表放大器电路以其高输入阻抗、高共模抑制比、低漂移等特点在传感器输出的小信号放大领域得到了广泛的应用。为此，我们设计了四种仪用放大器的方案。如上图是一个典型的仪用放大器是三运放结构，它是由运放A1，A2按通向输入接法组成第一级查分放
