基于单片机数字电压表电路设计外文文献原稿和译文

外文文献原稿和译文

原稿

Front side

Copyright of this circuit belongs to smart kit electronics. In this page we will use this circuit to discuss for improvements and we will introduce some changes based on original schematic

General Description

This is an easy to build, but nevertheless very accurate and useful digital voltmeter. It has been designed as a panel meter and can be used in DC power supplies or anywhere else it is necessary to have an accurate indication of the voltage present. The circuit employs the ADC (Analogue to Digital Converter) I.C. CL7107 made by INTERSIL. This IC incorporates in a 40 pin case all the circuitry necessary to convert an analogue signal to digital and can drive a series of four seven segment LED displays directly. The circuits built into the IC are an analogue to digital converter, a comparator, a clock, a decoder and a seven segment LED display driver. The circuit as it is described here can display any DC voltage in the range of 0-1999 Volts.

Technical Specifications - Characteristics

Supply Voltage: ............. +/- 5 V (Symmetrical)

Power requirements: ..... 200 mA (maximum)

Measuring range: .......... +/- 0-1,999 VDC in four ranges

Accuracy: ....................... 0.1 %

FEATURES

Small size

Easy construction

Low cost.

Simple adjustment.

Easy to read from a distance.

Few external components.

How it Works

In order to understand the principle of operation of the circuit it is necessary to explain how the ADC IC works. This IC has the following very important features: Great accuracy.

It is not affected by noise.

No need for a sample and hold circuit.

It has a built-in clock.

It has no need for high accuracy external components.

Schematic (fixed 16-11-09)

7-segment display pinout MAN6960

An Analogue to Digital Converter, (ADC from now on) is better known as a dual slope converter or integrating converter. This type of converter is generally preferred over other types as it offers accuracy, simplicity in design and a relative indifference to noise which makes it very reliable. The operation of the circuit is better understood if it is described in two stages. During the first stage and for a given period the input voltage is integrated, and in the output of the integrator at the end of this period, there is a voltage which is directly proportional to the input voltage. At the end of the preset period the integrator is fed with an internal reference voltage and the output of the circuit is gradually reduced until it reaches the level of the zero reference voltage. This second phase is known as the negative slope period and its duration depends on the output of the integrator in the first period. As the duration of the first operation is fixed and the length of the second is variable it is possible to compare the two and this way the input voltage is in fact compared to the internal reference voltage and the result is coded and is send to the display.

All this sounds quite easy but it is in fact a series of very complex operations which are all made by the ADC IC with the help of a few external components which are used to configure the circuit for the job. In detail the circuit works as follows. The voltage to be measured is applied across points 1 and 2 of the circuit and through the circuit R3, R4 and C4 is finally applied to pins 30 and 31 of the IC. These are the

input of the IC as you can see from its diagram. (IN HIGH & IN LOW respectively). The resistor R1 together with C1 are used to set the frequency of the internal oscillator (clock) which is set at about 48 Hz. At this clock rate there are about three different readings per second. The capacitor C2 which is connected between pins 33 and 34 of the IC has been selected to compensate for the error caused by the internal reference voltage and also keeps the display steady. The capacitor C3 and the resistor R5 are together the circuit that does the integration of the input voltage and at the same time prevent any division of the input voltage making the circuit faster and more reliable as the possibility of error is greatly reduced. The capacitor C5 forces the instrument to display zero when there is no voltage at its input. The resistor R2 together with P1 are used to adjust the instrument during set-up so that it displays zero when the input is zero. The resistor R6 controls the current that is allowed to flow through the displays so that there is sufficient brightness with out damaging them. The IC as we have already mentioned above is capable to drive four common anode LED displays. The three rightmost displays are connected so that they can display all the numbers from 0 to 9 while the first from the left can only display the number 1 and when the voltage is negative the ?-?sign. The whole c ircuit operates from a symmetrical ρ 5 VDC supply which is applied at pins 1 (+5 V), 21 (0 V) and 26 (-5 V) of the IC.

Construction

First of all let us consider a few basics in building electronic circuits on a printed circuit board. The board is made of a thin insulating material clad with a thin layer of conductive copper that is shaped in such a way as to form the necessary conductors between the various components of the circuit. The use of a properly designed printed circuit board is very desirable as it speeds construction up considerably and reduces the possibility of making errors. To protect the board during storage from oxidation and assure it gets to you in perfect condition the copper is tinned during manufacturing and covered with a special varnish that protects it from getting oxidised and also makes soldering easier.

Soldering the components to the board is the only way to build your circuit and

from the way you do it depends greatly your success or failure. This work is not very difficult and if you stick to a few rules you should have no problems. The soldering iron that you use must be light and its power should not exceed the 25 Watts. The tip should be fine and must be kept clean at all times. For this purpose come very handy specially made sponges that are kept wet and from time to time you can wipe the hot tip on them to remove all the residues that tend to accumulate on it.

DO NOT file or sandpaper a dirty or worn out tip. If the tip cannot be cleaned, replace it. There are many different types of solder in the market and you should choose a good quality one that contains the necessary flux in its core, to assure a perfect joint every time.

DO NOT use soldering flux apart from that which is already included in your solder. Too much flux can cause many problems and is one of the main causes of circuit malfunction. If nevertheless you have to use extra flux, as it is the case when you have to tin copper wires, clean it very thoroughly after you finish your work.

In order to solder a component correctly you should do the following:

Clean the component leads with a small piece of emery paper.

Bend them at the correct distance from the component’s body and insert the component in its place on the board.

You may find sometimes a component with heavier gauge leads than usual, that are too thick to enter in the holes of the p.c. board. In this case use a mini drill to enlarge the holes slightly. Do not make the holes too large as this is going to make soldering difficult afterwards.

Take the hot iron and place its tip on the component lead while holding the end of the solder wire at the point where the lead emerges from the board. The iron tip must touch the lead slightly above the p.c. board.

When the solder starts to melt and flow wait till it covers evenly the area around the hole and the flux boils and gets out from underneath the solder. The whole operation should not take more than 5 seconds. Remove the iron and allow the solder to cool naturally without blowing on it or moving the component. If everything was done properly the surface of the joint must have a bright metallic finish and its edges

should be smoothly ended on the component lead and the board track. If the solder looks dull, cracked, or has the shape of a blob then you have made a dry joint and you should remove the solder (with a pump, or a solder wick) and redo it.

Take care not to overheat the tracks as it is very easy to lift them from the board and break them.

When you are soldering a sensitive component it is good practice to hold the lead from the component side of the board with a pair of long-nose pliers to divert any heat that could possibly damage the component.

Make sure that you do not use more solder than it is necessary as you are running the risk of short-circuiting adjacent tracks on the board, especially if they are very close together.

When you finish your work, cut off the excess of the component leads and clean the board thoroughly with a suitable solvent to remove all flux residues that may still remain on it.

0 - 2 V ............ R3 = 0 ohm 1%

0 - 20 V ........... R3 = 1.2 Kohm 1%

0 - 200 V .......... R3 = 12 Kohm 1%

0 - 2000 V ......... R3 = 120 Kohm 1%

When you have finished all the soldering on the board and you are sure that everything is OK you can insert the IC in its place. The IC is CMOS and is very sensitive to static electricity. It comes wrapped in aluminium foil to protect it from static discharges and it should be handled with great care to avoid damaging it. Try to avoid touching its pins with your hands and keep the circuit and your body at ground potential when you insert it in its place.

Connect the circuit to a suitable power supply ρ 5 VDC and turn the supply on. The displays should light immediately and should form a number. Short circuit the input (0 V) and adjust the trimmer P1 until the display indicates exactly ?0?.

If it does not work

Check your work for possible dry joints, bridges across adjacent tracks or soldering flux residues that usually cause problems.

Check again all the external connections to and from the circuit to see if there is a mistake there.

See that there are no components missing or inserted in the wrong places.

Make sure that all the polarised components have been soldered the right way round.

Make sure the supply has the correct voltage and is connected the right way round to your circuit. - Check your project for faulty or damaged components.

Sample Power supply 1 Sample Power Supply 2

译文

引言

这是一个很容易建立并且非常准确和有用的数字电压表。它被设计成一个面板仪表，可用于直流电源供应器或其他需要有一个准确电压指示的地方。该电路采用的ADC（模拟数字转换器）集成电路CL7107由Intersil公司生产。该IC采用40引脚的情况下整合了所有必要的电路模拟信号转换为数字，可以直接驱动4个7段LED显示。在IC中内置的电路是数字转换器，比较器，一个时钟，一个解码器和一个7段LED显示驱动器模拟。在这里它描述了一个可以显示在0-1999电压范围的直流电压电路。

LED显示屏数字电压表技术规格 - 特征

电源电压：.............+ / - 5V（对称）。

电源要求：.............200mA（最大）。

测量范围：.............+ / - 0-1,999V在四个范围。

精度：.................0.1％。

特征：

小尺寸。

简易建筑。

成本低。

简单的调整。

易于读取距离。

很少的外部元件。

数字电压表的基本原则

为了了解电路的运作的原则，说明ADC的集成电路工程是必要的。该集成电路具有以下非常重要的特点：

准确性。

抗干扰性。

无需要一个采样保持电路。

它有一个内置的时钟。

它不需要精度高的外部元件。

一个模拟数字转换器(ADC)，从现在起更好的称为双斜率转换器或集成转换器。这种类型的转换器通常优于其他类型，因为它提供了准确，简洁的设计和它可以将相对不重要的噪音变得非常可靠。如果将电路分两个阶段描述，该电路的操作将更好的理解。在第一阶段的输入集成电压和最后阶段的输出集成电压中有一个电压与输入电压成正比。在预设的时间结束时，积分将到达内部基准电压以及输出电路会逐渐降低直至达到零参考电压水平。第二个阶段就是所谓的负斜率时期，其持续时间由第一阶段积分器输出而定。作为第一个操作时间是固定的，第二个变量的长度就可以比较两个这样的输入电压，其实是相对于内部参考电压，其结果是编码，然后发送到显示。

示意图（固定16-11-09）

7段显示器引出线MAN6960

这一切听起来很容易，但实际上它是一系列非常复杂的操作，这些都是由ADC集成电路作出了很少的外部元件，帮助它们用来配置工作的电路。详细的电路的工作原理如下。为了进行测量，需要将电压施加于电路的1和2点，最后通过电路的R3，R4和C4应用到集成电路的引脚30和31。从下图你可知这是该集成电路的输入(分别为高与低)。R1电阻的C1一起用来设置内部振荡器(时钟)，该设置约48Hz。在这个时钟速率大约有三个不同的每秒读数。连接集成电路引脚33和34之间的电容已被选定，以弥补由内部参考电压带来的误差，并保持稳定的显示。电容C3和电阻R5在一起的电路是输入电压的集成电路，同时它可避免任何使电路更快的分裂输入电压，从而使错误的可能性大大减少进而使电路更稳定。在没有输入电压时电容器C5强迫仪器显示为零。当输入为零时电阻R2和P1一起用来调整仪器在设置过程中显示为零。电阻R6的控制电流允许流经显示，以便使电路在没有损坏的前提下显示充分的亮度。至于我们上面已经提到的芯片它能够驱动4个共阳极LED显示屏。这三个最右边的显示器相连，使他们可以显示所有从0到9的数字，而从左边第一个只能显示数字1，当电压为负“-”的时候。整个电路工作，从对称ρ5伏直流电电源，这在引脚1(+5V)申请，21(0V)，26(-5V)集成电路。

数字电压表印刷电路板的加工

首先让我们考虑建立一个印刷电路板上的电子电路的基础知识。该印刷电路板是由薄绝缘铜的导电复合材料薄层形成，这样以形成电路之间的各组成部分的

必要的导体。一个设计完善的印刷电路板是非常可取的，因为它大大加快了加工，并大大减少了决策失误的可能性。为了保护印刷电路板在存储过程中被氧化和保证它到达你所要求的完美的条件，在生产过程中将铜镀锡的同时起表面还要覆盖一层特殊的漆，这样不仅防止了它被氧化，也使焊接更容易。

焊接的部件，印刷电路板是建立你的电路的唯一的方式和你在做板时很大程度上取决了你的成功或失败。这项工作也并不是很困难，如果你坚持有一些规则你应该没有问题。在你使用电烙铁时，其功率不应超过25瓦。它的尖应该是好的，并且必须时刻保持清洁。为此我们特地准备了一特制海绵并使其保持潮湿，这样可以不时擦拭热烙铁尖，从而去除积累在它上面的残渣。

如果烙铁尖不能清洗或更换，请勿用文件或砂纸弄脏或磨损其尖部。在市场上有许多不同类型的焊接剂，你应该选择一个优质的一个在其核心包含必需的流量的焊接剂，以保证每次焊接时都能完美的接合。

不使用助焊剂除了在你的焊接剂里已含有助焊剂。太多的流量可能会导致许多问题，也是电路故障的主要原因之一。但如果您必须使用额外的流量，因为它是在你不得不将铜线镀锡的情况下，将起彻底清除干净后你完成了你的工作。

为了焊接组件正确，您应该执行下列操作：

用一小块砂纸清洁清洁组件。

弯曲组件使它们之间有一合适的距离并插入在印刷电路板中的正确地位组成部分。

你有时可能会发现比起平常还会有重计部分，它将过于厚而不能进入个人电脑印刷电路板的孔。在这种情况下使用的小型钻孔略有放大。不要使孔太大，因为这将会使焊接困难。

拿着热铁将其尖端放在组件的一角上，同时将焊锡丝末梢放在尖端的一个点上。烙铁头必须触及略高于印刷电路板的地方。

当焊锡丝开始融化和流动等待它均匀覆盖孔周围的区域和通量疖并且焊料从下面流出。整个过程不应超过5秒。清除烙铁，让焊接剂自然冷却不吹，或移动组件。如果一切处理得当则表面联合处有一个光明的金属质感，其边缘应该是平滑的并且有一轨道面。如果焊料看起来暗淡无光，有裂痕的，或有一个气泡的

形状，那么你虚焊了和你应该清除焊接剂(用泵，或焊芯)然后重做它。

注意不要过热的轨道，因为它是很容易从其电路板上解除从而损坏电路板。

在你焊接一个敏感元件时，很好的做法是用一个长鼻子钳子夹着电路板组件的边缘进行热转移但是那样容易损坏组件。

确保你不使用过多的焊料是必需的，因为你正在冒着毗邻轨道短路的风险，特别是如果他们都非常接近时。

当你完成你的工作时，切断组件的多余部分和用适当的溶剂来彻底清除可能还留在电路板上的助焊剂残留物。

更换的电阻按照下表：

0 - 2V............ R3 = 0欧姆1％

0 - 20V........... R3 = 1.2千欧1％

0 - 200V.......... R3 = 12千欧1％

0 - 2000V......... R3 = 120千欧1％

当您完成所有的电路板上焊接和您确信一切正常，可以插入在其位芯片。该IC是CMOS类型于是对静电非常敏感。它有铝箔包裹以防止静电放电，并应小心处理，以免损坏它。尽量避免用你的手接触引脚，并且保持地面电路和你的身体电位在你插入的位置。

电路连接到一个合适的电源ρ5伏直流电上，开启电源。在光显示区应立即形成一个数字。短路输入（0V）和调整微调小屏幕显示，直到完全去掉0。

故障检查简介

检查您可能造成的虚焊，跨越邻近轨道或助焊剂残留物的桥梁工作，通常会造成问题。再次检查所有的电路和外部连接，看看是否有一个错误。

看是否有任何组件丢失或错误的地方插入：

确保所有的两极分化组件已被焊接正确。

确保供应具有正确的电压，以正确的方式连接到你的电路上。

检查您的故障或损坏的部件项目。

样品电源1 样品电源2