[Digital Circuit] Eight-way Intelligent Answering Device Design

1Project Introduction

  This is an eight-way answering machine developed based on CD4511BE . It can accurately, fairly and intuitively determine the number of the priority answerer, making knowledge competitions, cultural and sports entertainment activities (answer contests) more fair and just.

2 Overall design plan

  The overall block diagram of the eight-way answering machine project system is shown in Figure 2-1 . It is powered by a USB-5V power supply. The control part is driven by the CD4511BE latch decoder. When the answering button is pressed, the CD4511BE will give priority to latch the first pressed button. The button information, the digital tube displays the corresponding number, and the NE555 timer circuit works to make the buzzer sound an alarm. Press the reset button to reset and clear, so that you can continue to answer.

Figure 2-1 Overall block diagram of the eight-way answering machine system

3 Circuit Principle

  The design of the eight-way intelligent answering machine is mainly composed of five module circuits: power input, latch decoder drive control, answering and reset switch, digital tube display and timer driven buzzer sound alarm. The circuit principles of each module are analyzed below. .

3.1 Power circuit

 The power part is mainly a Micro USB female socket as the power input port, SW1 is a toggle switch, and C2/C3 are used as power filter capacitors. The USB interface is the only chip component in the entire project design.

Figure 3-1 Power input circuit

3.2 Switch circuit

  The switch array circuit is composed of eight buttons and switch tubes, and the answering buttons are used by competitors. The switch is a normally open type. When the switch is pressed, the switch is closed for answering; when the switch is released, the switch automatically pops out. The reset button is used by the host. When the reset button is pressed, BI# is pulled to low level, the display is cleared, and the circuit is in a waiting-for-answering state and enters the next round of answering.

Figure 3-2 Switch circuit

3.3 Control circuit

  The main control uses a CD4511BE latch decoder, which converts a certain switch information into the corresponding 8421BCD code, latches the switch information that is prioritized to answer, and prevents interference caused by other switch triggers. Then through encoding and decoding, the required logical state encoding input is provided for the digital display circuit of the digital device. LE works at a low level, and is disabled when connected to a high level, so connect the LE pin directly to a pull-down resistor in series with the ground; BI# works normally at a high level, and the display is cleared when it is a low level, so the BI# pin is connected to 5V and A reset button is connected to the ground. When the reset button is pressed, BI# is pulled low. According to the function table of CD4511BE , the display is cleared; LT# works at a high level, so connect the LT# pin to 5V ; inputs A~D correspond to The output a~g digital tube font display shows that the function table of CD4511BE is shown in Figure 3-4 .

Figure 3-3 Control circuit

Figure 3-4 Function table of CD4511BE

3.4 Display circuit

  The display circuit consists of a 1 -bit common cathode digital tube and 7 pull-up resistors. It receives the logic state from the CD4511BE latch decoder, lights up the digital tube accordingly, and displays the number of the priority responder. When the a~g inputs are high level, the corresponding digital tube segments are lit. For example, the digital tube displays the number 1 ( the inputs of b and c are 1 , the digital tubes light up the b and c segments accordingly; the rest are 0 , and the other digital tube segments do not light up. Bright).

Figure 3-5 shows the circuit

3.5 Alarm circuit

  The alarm circuit is composed of NE555 timer, buzzer and other components. When the answer button is pressed, when a pulse arrives, the NE555 timer enters a temporary steady state and outputs a high level to drive the buzzer to sound an alarm, indicating that the answer is successful. . After maintaining the temporary steady state for a period of time, it will automatically return to the steady state, and the buzzer will return to a low level and stop sounding.

Figure 3-6 Alarm circuit

4 Simulation diagram design

4.1 Simulation diagram creation

 You can switch the Easy EDA standard version mode to the simulation mode, create a project and name it [Digital Circuit] Eight-channel Intelligent Responder Design . Carry out simulation design verification function for the eight-way answering machine , and name the simulation diagram file: SIM_Eight -way intelligent answering machine design. Draw a circuit simulation diagram based on the following circuit.

图4-1 SIM_八路智力抢答器设计

  在选择仿真器件时需要注意只能在仿真模式下的仿真基础库宇仿真扩展库中的系统库器件进行调用，用户贡献的仿真库不确保能够正常仿真运行。

  在该项目中的所有仿真器件都可以在仿真库中进行调用。在绘制仿真图时有以下几点注意事项：

  （1）所有的仿真电路都必须要有仿真电源和接地；

  （2）555定时器放置后可以按键盘的X键进行翻转，得到3脚朝右的样式；

  （3）示波器连接输出接口可以用网络标签、网络端口或者直接接线三种方式；

  （4）参考图波形与要求不符时，需要自行调整滑动变阻器参数得到所需结果。

4.2 仿真验证

  点击仿真后，蜂鸣器的模拟发声可使用示波器查看仪表功能观察波形情况，移动T1和T2时间轴，查看波形周期与频率大小，峰值为蜂鸣器发声时的工作电压。可按抢答键进行模拟抢答，RSTER为复位键，按下即显示清零，进入下一轮待抢答状态，需要注意的是每次调整参数后需要重新点击运行仿真，运行仿真的快捷键为F8。

5 原理图设计

5.1 原理图创建

  把仿真图保存后将仿真模式切换为标准模式，在同一工程下新建原理图命名为：SCH_八路智力抢答器设计。根据以下电路进行绘制电路原理图。

图5-1 SCH_八路智力抢答器设计

5.2 器件选型

  在本项目的元器件选型中，所有器件可直接在立创EDA的元件库中进行搜索。如果对元器件不熟悉，也可以通过复制物料中的商品编号进行搜索（每一个元器件在立创商城都有唯一的商品编号），如果出现物料缺货情况，亦可选择其他可替换物料，通过以上电路的分析，相信聪明的你对各个元器件在电路中的作用有所了解，那么更换个别物料也不会影响到电路的工作性能的，了解电路工作特性后，电路选型也就变得简单了。

图5-2 元器件搜索示意图

图5-3 通过商品编号搜索示意图

5.3 物料清单

6 PCB设计

  完成原理图设计后，经过检查电路与网络连接正确后点击顶部菜单栏的 “设计” → “原理图转PCB”（快捷键为Alt+P），随即会生成一个PCB设计界面，可先暂时忽略弹出的边框设置，然后将PCB文件保存到工程文件中，并命名为：PCB_八路智力抢答器设计。

6.1 边框设计

  在绘制PCB前需根据个人意愿以及元器件数量所占空间确定PCB的形状及边框大小，若无特殊外壳要求，一般设计成矩形、圆形以及正方形。在设计该项目时，秉承着大小合适，美观大方的原则，我们在顶部工具菜单栏下的边框设置选型中设定了一个长为90mm、宽60mm、圆角半径为2mm的圆角矩形。实际板框大小会随着布局布线中进行调整，如果太小可适当放大，太大也可缩小边框，风格样式可自由发挥，但尽量控制在10cm*10cm之内，这样就可以到嘉立创免费打样啦～

图6-1 边框设置

图6-2 八路智力抢答器设计边框示意图

6.2 PCB布局

  在绘制完板框外形后，接下来进行PCB设计的第二步，对元器件进行分类和布局，分类指的是按照电路原理图的功能模块把各个元器件进行分类，图中有很多模块电路，但哪一些元器件是连到一起的呢，这里需要我们用到立创EDA所提供的布局传递功能，首先确保PCB工程已保存到原理图文件的同一个工程文件夹中，然后框选原理图中的某一电路模块，比如选中按键电路，然后点击顶部菜单栏中的 ”工具” → ”布局传递“ （快捷键为Ctrl+Shift+X），PCB页面所对应的元器件就好进行选中并按照原理图布局进行摆放，使用这个方法将各电路模块进行分类后依次摆放在前面所放置的边框中。

  在布局的时候注意摆放整齐，可根据飞线的指引进行摆放，按照原理图信号的流向和器件连接关系进行摆放，是可以把原理图器件摆放非常整齐的，在布局的过程中注意显示及控制位置，比如数码管放置在中间偏右上方，根据视听效果，蜂鸣器紧挨靠在数码管右侧。按键根据使用习惯全部摆放在PCB下方。电源输入、开关、放置在PCB的最左边边缘。布局参考如图5-3所示。

图6-3 PCB布局参考图（飞线已隐藏）

6.3 PCB走线

  接下来进行PCB设计的第三步：PCB走线，全称为印刷电路板布线（PCB LAYOUT）。由于电路板有顶面与底面两个面，在PCB走线也就可以分为顶层和底层走线，其中顶层走线默认是红色线，底层为蓝色线，也可按照个人喜好设置其他颜色，走线也就是在电路板中按照飞线连接导线，将相同的网络连接起来即可。

  首先选择层与元素中要走线的层，然后点击导线工具进行连线（快捷键为W）。看似简单的连连看，其中需要我们耐心的进行调整，元器件的摆放布局也会影响走线的难度，所以还需要在走线过程中进一步调整布局，进一步优化。前面所介绍的PCB布局相当于是在给走线做铺垫，布局好了，走线也就自然顺畅了。在该项目的走线中提供以下几点参考建议：

（1）电源线设置为25mil，信号线设置为15mil宽度

（2）走线以顶层走线为主，走不通的可以切换到底层进行连接

（3）走线过程中优先走直线，需要拐弯的地方以钝角或圆弧拐弯为主

（4）最后加上泪滴，添加丝印标记该PCB板的尺寸以及接口功能

布线参考如图5-4所示，初次设计可参考下图进行走线，也可自由设计，属于你的八路抢答器。

图6-4 PCB顶层走线参考图

图6-5 PCB底层走线参考图

6.4 覆铜与丝印

   PCB走线画完后进行覆铜，就可以连接好GND网络。丝印字符遵循从左到右，从上往下的原则。对电解电容、蜂鸣器等极性的元器件在每个功能单元内应尽量保持方向一致。标注工程名称与logo。

图6-6 PCB顶层覆铜与丝印参考图

图6-7 PCB底层覆铜与丝印参考图

7 焊接与调试

7.1 硬件焊接

  After getting the board and components, you should first check whether the materials are missing or missing, and then proceed with welding after checking them. The welding principle is to start low and then high. First weld the USB , resistor and diode to the board, then weld the capacitor , transistor and IC holder, and finally weld the buttons , buzzer and digital tube. After completing the welding, plug in the NE555 and CD4511 chip . The welding method of direct plug-in components is shown in the figure below. Pay attention to the correct position when welding, check whether the component model is correct, and whether the tin wire is soldered to avoid affecting the circuit performance and causing the circuit to not work properly.

Figure 7-3  PCB assembly diagram

Figure 7-4  Unsoldered PCB board

Figure 7-5 PCBA physical diagram

Figure 7-6 PCB-3D preview

7.2 Hardware debugging​ 

  Insert the data cable into the Micro USB to power the eight-way answering machine project. Move the switch to the OPEN state, the power indicator light will light up, the digital tube will display zero, and the answering machine will enter the waiting state. When the answer key is pressed, the buzzer will sound. Adjust the resistance of the potentiometer so that the buzzer sound reaches the best state. The digital tube displays the corresponding number of answer keys. When the reset button is pressed, the digital tube display is cleared. The answering machine enters the next round of waiting state.

Figure 7-7 Working diagram of the eight-way intelligent answering machine