[Original tutorial of black gold] [serialization] [iboard Electronic School] [〇] Part 2 circuit diagram and Printed Circuit Board

I,What is circuit schematic

The circuit schematic diagram is a schematic diagram that uses graphical symbols in a certain order to describe the basic connection relationship between the circuit and the device, regardless of the actual location or physical form, circuit diagram or schematic diagram.

1Basic schematic Elements

A circuit diagram consists of schematic symbols, electrical connections between symbols, annotations, and other basic elements. Schematic diagram is the most direct technical means for communication between engineers, technical archiving of enterprises, and collaboration between colleagues. Therefore, the design principle diagram should not only consider the correctness of the principles, but also pay attention to its ease of use and standardization, do not create ambiguity.

The schematic symbol represents the pin distribution of electronic components in a two-dimensional plane. It represents the pin distribution or principle of electronic components, and does not have physical structure or size characteristics. Schematic symbols are composed of three parts: pins, principles, and annotations. Let's take the symbol of the luminous second-level tube as an example to illustrate the structure of the schematic symbol, as shown in figure 1.

The electrical connections between schematic symbols can be connected through nodes, connections, bus, pages, ports, and other methods. There are some differences between different design software, but the general idea and meaning are basically the same.

A good schematic diagram looks well organized and easy to understand. Therefore, necessary annotations and comments are a part of it. Engineers usually use key comments, modular segmentation, and functional paging modes to design the schematic diagram, making it easy to understand.

2Commonly used circuit schematic EDA software

ProtelSeries:The Protel series is an EDA software that has a long history and has many users in China. It occupies most of the schematic diagram and Printed Circuit Board (PCB) teaching courses in Chinese universities. Later versions of PROTEL, alicloud designer, have developed rapidly in recent years and have now reached version 10. It is an EDA software commonly used by electronic engineers in China.

Pads:Pads is also a common EDA software. It consumes less resources and is fast. It provides powerful interactive layout and wiring functions, which are easy to learn and easy to use, it is also one of the most commonly used EDA software.

Orcad capture:Orcad capture, as an industrial standard schematic input method, is one of the most popular schematic input tools in the world today. It provides a complete and adjustable schematic design method, and has a simple and intuitive user design interface. Orcad Capture CIS has a powerful component information system that can manage component databases online and centrally, greatly improving the efficiency of circuit design. The schematic diagram of iboard Emy is designed using orcad capture software.

Kicad EDA suite:Kicad is a cross-platform and open-source EDA tool that provides a compatible development environment for MS-windows and many Linux platforms (such as Debian, Ubuntu, fedora, Gentoo, and slackware, is an excellent tool worthy of recommendation. Its URL is: http://kicad.sourceforge.net /.

3Orcad capture simple procedure

The schematic diagram of iboard Electronic School is drawn through orcad capture 16.3. Next we will illustrate the basic steps of the schematic diagram through simple steps.

Installation:Orcad software has powerful functions, so its installation file is also very large. After the attached CD is installed, we can see the shortcut on the desktop (or the Start Menu), double-click to open the software. Shows the interface.

New project:After the installation is complete, click File → new → project... To create a project, as shown in.

The new project dialog box is displayed, as shown in. Enter the project name in the name column, select schematic (to create a new schematic), and select the path where the project is stored in the location, you can create a project folder before creating a project. You are not advised to use Chinese characters as the folder name. After entering and setting, click OK to create an empty project.

Shows the new project schematic management. design resources are the design resources, which contain the schematic file (*. DSN, design cache, and library. You can right-click the library and add file to add your own library. The extension of the symbol library is olb. As shown in. Here we have added my own database wfj. olb.

Schematic diagram:Double-click page1 to open the first page of the schematic diagram. Of course, you can add or rename the schematic page. Wfj. olb library, which has been added above. In addition, the system library file connector is also required. olb and discrete. olb. Both databases are in the orcad capture installation directory. You need to add them on your own.

After entering the drawing area, choose place> part to place the symbol (or press the shortcut key pp), and place the power symbol (or press the shortcut key PF) by selecting place> power ), place the place symbol (or the shortcut key PG) by selecting place → ground, and select place → wire to place the line (or shortcut key W ), select place> Junction to place nodes (or shortcut key J), and choose place> no connect to place ports not connected (or shortcut key X ).

Here we take the minimum single-chip microcomputer system as an example to draw a simple schematic. This schematic diagram contains the following types of symbols:

Symbol name

Database

PCBLibrary

Secondary note

PP2

Wfj. olb

Power_plug

Power plug

EC

Wfj. olb

Aec6.5

Electrolytic Capacitor

R

Wfj. olb

0603

Resistance

C

Wfj. olb

0603

Porcelain chip Capacitor

Header 3

Connector. olb

Xh3pl

Mcu uart download Port

LED

Wfj. olb

Led0603

Light emitting second-level Tube

Stc10l04

Wfj. olb

TQFP-44

Single Chip Microcomputer

ZTA

Discrete. olb

Cy_2s

Crystal Oscillator

DCOM

Wfj. olb

-

System digital location

VCC

Wfj. olb

-

System Power Supply

As shown in.

Double-click the device and add the PCB Encapsulation by using the "PCB footprintf" property item in the editor. The PCB encapsulation of each component is shown in the table above. After the schematic diagram is edited, we need to re-label all the symbols and perform DRC checks. This is not described here.

Export the Protel network table:After the schematic diagram is drawn, We need to export the network table for the PCB design software. Orcad's powerful network Table processing capability enables it to be connected to most PCB software on the market. Here we use Protel 99se as an example to export the network table. To export a network table, choose tools> Create netlist to open the export network Table dialog box, as shown in. Select the other option, select orprotel2.dll format, and click OK. If there are no errors in the process, you can export the network Table file orcad_demo.net perfectly and store it under the outputs tree structure of project file management. So far, the schematic diagram has been drawn.

II,Printed Circuit Board

Printed Circuit Board, also known as printed circuit board or PCB (Printed Circuit Board), is the support body of electronic components and is also the provider of the connection of electronic components. It uses the printing corrosion process to complete the line. At present, the PCB process is very mature.

1, Printed circuit board composition

Printed circuit boards include the following components:

Line and drawing (pattern ):Line as a way of connecting components, the drawing is to meet the special needs of the pad, a large area of copper, fill, etc., the line and the map is made in the same process steps.

Dielectric ):To connect, volume and signal, printed circuit boards generally contain multiple layers. The layers are connected by the dielectric layer, commonly known as substrates. Currently, the commonly used substrates include paper-based, epoxy fiberglass fabric, composite substrates, and special substrates.

Through Hole/):The passing hole is the electrical connection between the layer and the layer. In the multi-layer board, the passing holes that are not fully transparent are called blind holes.

Solder Mask (Solder Mask ):In order to avoid short-circuits in non-connected parts, we need to mask welding resources (commonly known as Green Oil) in addition to the welding pad and other places to prevent short-circuits. The color of the solder mask is varied. In addition, the area occupied by the solder mask is large, so we usually see that the PCB color is the color of the solder mask.

Silk Screen ):The printing layer used to mark the physical border of the device and the comments is called the silk screen layer. The Silk Screen Layer facilitates welding, debugging and assembly. The Silk Screen Layer does not participate in electrical connections, but only comments, so it is an optional component. For easy identification, the silk screen layer is generally white.

Surface Finish ):Because the copper surface is prone to oxidation, resulting in poor welding, so in the PCB production process, the Solder Pad is usually used for tin spraying, gold plating, gold sinking and other processes. In order to ensure the smoothness of the pad, the iboard Electronic School adopted the gold Sinking Process.

2Design Steps of PCB based on protel99se

Install software:Install the protel99se software on the CD. After that, there will be an icon on the desktop. We double-click it to open the software, as shown in.

Project Creation:Click File> New to create a new engineering database, as shown in. Here we need to name the project file, such as pcb_demo.ddb, and select the appropriate local path.

Click "OK" to go to the Project Management page. Double-click the documents directory. Right-click the "new" feature to open the new file dialog box. As shown in. Select the PCB document and click "OK ". After the PCB document is created, we need to import the network table generated by the orcadcapture schematic tool to the project. Method: Right click → import to import the network table (*. Net) file.

Import a network table:Double-click the PCB File to enter the PCB editing mode. First, we need to import the network table, and enter the network table management dialog box through design → netlist Manager (or shortcut key DN), as shown in.

Select Browse to select the file (orcad_demo.net) that has just been imported to the network Table file. If the PCB encapsulation of the schematic diagram is correct, it can be executed smoothly ,. Click execute to import the network table.

In this way, our devices are completely imported into the PCB file. It is worth noting that the current view of the PCB may not be suitable for viewing the imported devices. We use the shortcut key VF to display all the devices, you can also use page up to zoom in the display view and page down to zoom out the display view.

At the bottom of the PCB editing page, you can select layers, as shown in the following table:

Graph Layer

Name

Meaning

Tolayer

Top layer

PCB top-Layer Wiring Layer

Bottomlayer

Bottom Layer

PCB underlying wiring Layer

Machical1

Mechanical Layer 1

Mechanical Layer 1

Topoverlay

Silk Screen Layer

Silk Screen Layer, used for annotation or Component symbol marking

Keepoutlayer

Disable cabling Layer

Generally used for PCB border cutting in China

Multilayer

Multi-Layer

Multilayer, usually used for passing through holes

Draw borders:Different layers represent different meanings during plotting. First, we need to draw a border for the PCB. We need to switch the layer to the keepoutlayer. Here we draw a square of 50cmx 50cm as the border. As shown in.

Layout:Through the operation, the device is reasonably distributed within the border for the layout stage. Here, we need to observe the constraints such as reasonable confidentiality, close electrical connection, and modular functions. The layout has a direct impact on the following steps. In general PCB design processes, the layout requires at least 1/3 of the workload. As shown in.

Wiring:Wiring is an important part of the entire PCB drawing and also the most labor-intensive part. Currently, we use the imperial unit (MIL) for the line width. Generally, the number of lines can be changed from 6 ~ 12mil. The analog circuit is set to 10 ~ based on the current flow ~ 20 mil, power line (power supply, ground, etc.) trunk must be at least 30 mil. The shortcut key PT is used for cabling. Because the circuit is simple, we can use a dual panel (that is, a two-layer board) to complete the function. The available layers are toplayer (top layer, red line here) and bottomlayer (bottom layer, blue line here ).

Placed through the hole:If the underlying layer and the top layer need to be electrically connected, we need to place the Via, And the shortcut key is PV. The passing hole has two attributes: the outer diameter and the internal diameter. Here we take 30mil and 15mil.

Copper clad:Because this circuit is relatively simple and is a digital circuit, we use the top layer to strip and the bottom layer to cover a large area of copper (as a system ). The copper-coated method is the shortcut pg. after entering the dialog box for copper-coated, select DCOM and set the layer to bottomlayer, as shown in.

DRC:PCB wiring is a meticulous task. It is difficult to see whether the wiring is complete and whether there are any parts that do not comply with the rules by human eyes. Therefore, after the wiring is complete, we need to do the DRC (design rule check ), to check for any flaws. The command of DRC is the TD shortcut key. After you press it, the following dialog box is displayed. we press the run check button to perform the DRC operation. After the operation, a report is generated, through reports, we can detect some properties and errors that do not conform to the rules (such as short circuit, open circuit, device overlap, line width mismatch and requirements, Solder Pad noncompliance and other attributes, which can be changed, for details, refer to other materials ).

So far, we have completed a simple PCB process. Shows the final completion chart.

Communication Method:

QQ group:

Iboard Electronic School Group [A]: 204255896 (500 people, full)
Iboard Electronic School Group [B]: 165201798 (super group of 500 people)
Iboard Electronic School Group [c]: 215053598 (200 senior group)
Iboard Electronic School Group [d]: 215054675 (200 senior group)
Iboard Electronic School Group [e]: 215055211 (200 senior group)
Iboard Electronic School group (F): 78538605 (200 senior group)