Blog  /  PCB Schematic: A 2D Diagram for Component Functions and Connections

PCB Schematic: A 2D Diagram for Component Functions and Connections

Regardless of the circuit board type, the first step when you want to make one is to develop a schematic. The diagram lays out your idea in a simple layout for easier understanding before proceeding to other complex design and manufacturing phases later. So what is a PCB schematic, and how do you make one? We have looked at all this in detail below, so take a look!

 

PCB Schematics vs. PCB Designs

 

A PCB schematic is a simple 2-dimensional circuit design that shows the functions and connections between components. It is usually the first step in designing a PCB project and uses standardized symbols to define the real circuit connections.

However, the blueprint does not specify the exact location of the components. Its primary purpose is to show the connections.

On the other hand, a PCB design is a 3-dimensional board layout that shows the exact component location. The PCB design process comes right after the PCB schematic is complete. It defines the physical structure of the circuit, including the hole layout.

 

PCB schematic and design diagrams placed side by side in DesignSpark design software

PCB schematic and design diagrams placed side by side in DesignSpark design software

Source: Wikimedia Commons

 

By focusing on component location, the design process looks more into performance. After the two phases, you can send the design to a PCB manufacturer for fabrication.

 

Guidelines to Draw a PCB Schematic Diagram

 

These guidelines will help you design a successful schematic design.

 

Page Size Selection

 

Most design tools have different page sizes, but A4 is the most common. As a designer, you should pick a page size that suits the size of your circuit design.

 

Page Naming Convention

 

Separate the logic blocks of the schematic using the pages, then name each page using letters or numbers. After doing so, you can place the pages in a naming convention order, such as:

  • 1_Block Diagram
  • 2_Power Supply
  • 3_MCU Interface
  • 4_Memory Interface
  • 5_Revision History

Or replace the numbers with letters.

 

Grid Setting

 

A grid system gives some reference, enabling the designer to refer to the parts correctly when connecting them. To help probe the nets in the analysis stage, you must place the circuit components and connections on the grid.

 

Electronic components

Electronic components

 

Page Title Block

 

A page title block sits in the footer of the schematic page, and while not a must, it is good practice to fill in all the details. These include the following:

  • Update date
  • Page size
  • Document number
  • Revision
  • Name and function of the circuit
  • Company disclaimer

 

An A4 size schematic diagram. Note the page title block at the bottom right.

An A4 size schematic diagram. Note the page title block at the bottom right.

Source: Flickr

 

Notes/Comments

 

Like programming, notes and comments help explain the schematic pages to the person building the design and other designers. As a general rule, layout designers make notes on separate pages for complex circuit designs but comment on the same page in simple schematics.

 

A schematic diagram with notes at the bottom

A schematic diagram with notes at the bottom

Source: Wikimedia Commons

 

Revision History

 

A revision history tracks all changes made to the design pages, providing helpful information, such as the following:

  • Description and date of the changes
  • Author and reviewer name
  • Review comments

The history typically goes to the first or final page of the schematic.

 

Schematic Document Table of Contents

 

Since the schematic document has different topics, it is easier to get to a specific page using a table of contents. The table comes in handy if you have to get to a particular module in a large and complex design. However, you can skip this guideline if the schematic is simple.

 

Block Diagram

 

A block diagram shows the signal flow across different modules in the design. It simplifies the reviewer's work because it is easier to understand the schematic during the review process.

 

An Intel Edison block diagram

An Intel Edison block diagram

Source: Wikimedia Commons

 

Hierarchical Schematic Design

 

While a block diagram makes the design easy to understand, it might not be enough for complex circuits. Therefore, you need to use a hierarchical schematic to show the signal flow from one module to another.

 

Component Referencing

 

Component referencing is usually in the form of a table that shows the electronic components in use and their reference designators.

These designators get assigned as per the IEEE standard, and the recommended procedure is to name the components with their standard reference designators. On top of that, you should use capital letters to label the schematic symbols.

 

Symbol Generation

 

A schematic diagram consists of different electrical components (active & passive components) and connectors. Make sure you use the symbols in the standard library to represent these parts in the schematic. However, if you don't get the required ones, it is acceptable to create new symbols.

 

Electronic circuit symbols

Electronic circuit symbols

 

Net Connections

 

When two wires form a junction on the same electrical connection, each should have its junction dot.

 

A bridge rectifier. Note the junction dots

A bridge rectifier. Note the junction dots

Source: Wikimedia commons

 

It is best to embrace the net labeling conventions when drawing integrated circuit symbols and specific pins for easy readability. Also, adhere to the net labeling guidelines, off-page connections, and signal flow representation.

 

Component Placements

 

The placement of components is also a crucial part of the design process, and you should do it correctly to improve readability to the layout engineer.

 

Crystal Placement

 

Components linked to the crystal should always be nearby because the signals could be the high-frequency type.

 

DRC Check

 

Computer-Aided Design software offers a Design Rule Check (DRC) to check the physical and logical integrity of the design. You can do the checks live as you design online against all enabled design regulations.

 

Netlist Verification

 

Netlist files either have .txt or .mnl extensions, and you can generate them after the schematic design is complete and ready for importation in the layout.

MNL files are machine-readable, while TXT files show all the nets and connections between the component pins. Ensure you verify the traps manually to prevent design errors.

 

Bill of Material (BOM)

 

CAD software has a BOM creation feature. You can only generate a complete, sufficient BOM if the designer provides all the inputs in the tools when creating/importing library components.

 

Single BOM

Single BOM

Source: Wikimedia Commons.

 

Some of the BOM inputs include:

  • Manufacturing Part Number
  • Vendor Part Number
  • Vendor name
  • Package name

The general rule of thumb is to provide all the required information in the symbol creation stage.

 

Converting a Schematic into a PCB Layout

 

Designers usually use CAD software to convert a schematic into a PCB design consisting of ratlines and component footprints. Ratlines refer to electrical connections that will be physical later. To do the conversion:

  1. Open the schematic project in the control panel of Autodesk Eagle.
  2. Select the BRD/SCH icon to begin the conversion process. It will generate the board layout using the ratlines and components as guides to create copper traces, vias, copper pours, etc.
  3. If you get a warning saying that the BRD file does not exist, click "Yes" to create it from your schematic.

That's it. You will get a window that displays the following:

  • A white square outline showing the board's physical dimensions
  • All components resting outside the square outline
  • Multiple lines/air wires connecting the components

How to Convert PCB to Schematic Diagram?

 

Here are some of the ways to do the reverse of the process explained above.

 

How to Draw Circuit Diagrams According to Real Products?

 

Engineers often encounter problems locating the drawings required to repair legacy electronic products. Therefore, drawing the circuit diagram is necessary to analyze and improve the product. The process involves these steps:

  1. Identify and use the components with multiple pins and large volumes as references for drawing the electronic circuits.
  2. When printing the circuit board, label the components and pay attention to the serial number regularity. Label them according to the particular rules to ensure you don't make mistakes when drawing.
  3. Number the components to improve proofreading and analysis, which will prevent difficulties later. Make sure you mark all the vital parts to avoid missing them when drawing the PCB file.
  4. Distinguish the printed circuit board wires correctly with their layout positions, functions, and rules. These include the power, signal, and ground wires, plus others.
  5. Use transparent tracing paper to draw the sketch and mark it using colorful pens. Before sketching, try to find and use an existing diagram on paper as a reference to create some standard in your drawings, which will be helpful to beginners involved in your project.

The process is not complicated, but it might be to beginners due to a lack of experience.

 

Printed circuit board

Printed circuit board

 

Protel+PCB Convert Into Schematic

 

You can also use Protel PCB to convert a PCB into a schematic by using these steps:

  1. Begin by opening the PCB diagram, then click the "File-Export" menu to export the Protel network table. It should have "Serial.Net" as its abbreviated file name.
  2. Start the Omninet program, then pick "Protel" as the file input type. In Input File 1, browse to the location of the netlist file and select it (Serial.Net). For the output, pick EDIF as the file type, specify the name and path of the output file, then click the running icon. An output window should pop up. Click "Accept Data," then click "OK" after finishing, and "Done" to close the window. Exit Omninet.

 

Start E-Studio software and open the EDIF file created in step 2.

 

  1. Right-click on the Serial EDF file, then generate the schematics. A window should pop up and click "OK" on it.
  2. Regardless of the complexity of the circuit, the drawings have no hierarchy, so expect the single-plane graph to be highly detailed. Click on "File">"Save As," then pick the output format "OrCAD." Save as "Design V9.10" in the drop-down menu, then click "Save" and "OK" in the pop-up window that shows up.

 

A complex schematic diagram

A complex schematic diagram

Source: Wikimedia Commons

 

  1. Next, convert the OrCAD file into a Protel schematic, and Protel 2004 gives a better conversion effect. Launch the software, then open the DSN file (pick OrCAD Capture Design as the file type).
  2. Once you click "Open," you will get an error message, but the file conversion was a success. Click "Ok" to close the error pop-up window.
  3. Double click the "1.SchDoc" file, then select save it as a .sch file (schematic binary 4.0). Conversion is complete, and you can open the file in Protel 99Se.

However, it is crucial to note that the conversion is primarily helpful for PCBs with few components due to the lack of a hierarchy. Also, there will be no unconnected pins in the schematic, and the footprint information will disappear, so you must fill it again.

 

Convert Eagle Circuit Diagram to Altium Designer PCB Format

 

If you are using open-source hardware from manufacturers like Arduino, you can download the Eagle file on their website. Next, convert the file into a format that Altium Designer software can open.

 

An ATX2 Arduino microcontroller design diagram

An ATX2 Arduino microcontroller design diagram

Source: Pixabay

 

Use the following steps:

  1. Download the ULP file
  2. Place the file in the ULP folder in the Eagle installation directory
  3. Click the ULP command in the command toolbar
  4. In the pop-up dialog box directory, pick "export-Protel PCB.ulp," then open.
  5. Select a suitable path to save the converted PCB file
  6. Click "Save," then "Ok" in the dialog pop up box
  7. Open the saved PCB file in Altium Designer by double-clicking it.

 

A high bandwidth memory schematic diagram

A high bandwidth memory schematic diagram

Source: Wikimedia Commons

 

Schematic checklist

 

A schematic checklist helps to avoid any design error and should include the following:

  • Verify the pin numbering and labels of each component as per the datasheet
  • A polarity check on all polarized components
  • Check if there are any overlapping PINs and labels
  • Verify the BCE transistor terminals with the footprint package, datasheet, and schematic symbol
  • Validate the location, reference designators, and value of the components
  • Check the schematic symbol descriptions (Manufacturing Part Number, vendor part number, etc.)

 

Fritzing schematic view

Fritzing schematic view

Source: Wikimedia Commons

 

  • Look for off-page connectors.
  • Check for inter sheet reference.
  • Do decoupling capacitor checks for the integrated circuits and ground pin separation depending on the signal type (ground, digital, analog)
  • Quantity and part number BOM checks

 

Summary

 

There you have it! Even though some people use PCB schematic and PCB design interchangeably, the two are very different, as explained above. Therefore, if you have a PCB project, start by sketching the schematic, then make the design, and contact us with the final board layout to begin fabrication.