How to Create a Printed Circuit Board (PCB)(Section 3)

3. Schematic Capture

    Schematic capture software comes in several forms. In this application note, OrCAD Capture v9.10 will be used. Schematic capture allows the PCB designer to create an electronic schematic. This electronic schematic contains more information than its paper relatives. For example, every part symbol in Capture contains information telling what footprint the symbol is associated with.(Footprints are the symbols used in layout software to define the physical design of each component.)

    Capture parts symbols are used in a symbolic manner. Thus, the part symbol on Capture's screen does not show what the actual physical component looks like. It does allow the designer to connect all the components in a circuit and to test the workings of the circuit by exporting files to other software. For our purpose, Capture provides the starting point for creating a physical layout in layout software.

     A good way to begin learning Capture is through the Capture menu item Help→Learning Capture. This tutorial will do a good job of explaining the basics of Capture. For further help, look in the troubleshooting section found in the appendix of this document and search for your question under Help→Help Topics on Capture’s menu bar. In the following section of this application note, we will assume the reader has a basic familiarity with Capture.

Capture was used to create an electronic schematic of the optosensor circuit. First, the existing part libraries were searched for the necessary parts. A part symbol is needed for every component that will need to be drilled or routed in Layout. This means that a part symbol will be needed for things such as power connections. In this particular case, the optosensor circuit required a power connector that was not available in the Capture libraries. Thus, one was created using the process demonstrated in the Learning Capture tutorial. These part symbols were placed on the drawing area and wired together as they had been wired in the paper schematic and on the prototype board.

Once the optosensor circuit schematic was completed a netlist file was created for use in the physical layout software. This was done from the Project manager screen in Capture by selecting the name of the design, which in this case was “. optoencoder.dsn”. With this item highlighted, the menu item Tools→CreateNetlist…, was selected. In the displayed Create Netlist dialog box, the “Layout” tab along the top of the dialog box was selected. Here the netlist file name and location were specified and then created with the click of an OK. The netlist file in this case was called “optoencoder.mnl”. This file contained all the information necessary to begin the physical layout of the optosensor circuit.

    One important comment is that every part symbol used in Capture must have a footprint associated with it. The footprint property of the symbol may be edited by double clicking on the part symbol in the schematic and editing the footprint property on the parameter list.

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Section

1. Overview

2. Prototyping

3. Schematic Capture

4. Physical Layout

5. Physical Creation of PCB

6. Lessons Learned and Recommendations

7. Appendix