Schematic Capture

Schematic Capture is the process of creating your schematic inside an EDA.

2. Flat vs. Hierarchical Layout

As a designer, you have multiple options for schematic organization.  Which one you choose will depend on EDA software, personal preference, and design complexity.

The overall organization of your design can either be flat or hierarchical.  

Option 1:  Flat Schematic Layout -- This design technique is meant for simple circuits.  The entire schematic is drawn on a single page, or split on multiple pages for ease of reading.  Sheet symbols all exist on the same level.  You can directly connect pins and parts on different pages.  If you've ever made a schematic, you've likely made a flat schematic.  For simple designs, you can use a flat organization, but if you make anything with more than two or three ICs, you will want to learn to use hierarchical layout techniques.

Option 2: Hierarchical Schematic Layout -- This design technique is meant for every moderate or high complexity circuit.  Every circuit block is replaced with a new symbol that shows only the inputs/outputs/connections to other circuit blocks.  Pull-up resistors, power connections, bypass capacitors, and every other bit of housekeeping is still shown on the schematic page for that block, but they are not shown on the parent page.  This allows someone reading the schematic to quickly develop a high-level overview of the function of the circuit without being bombarded by little details.  Then when it is time to inspect the details, they can open up the page that contains that element.

This image shows a single hierarchical element.  From Altium's "Creating Hierarchical Design"

In a hierarchical design, a parent-page shows the high-level overview, and child pages show increasing amounts of detail.  Child pages can only connect to a parent page, they cannot share connections with other child pages (there's usually a way to make it happen, it's just discouraged for most use-cases).

Hierarchical Block Diagram

Image from Altium's "Creating Hierarchical Design" shows the relationship between the parent and the child pages.

There are other benefits of a hierarchical schematic.  

  • Multiple designers can easily contribute their individual child schematic to a parent design.
  • Circuit blocks (child pages) you create for one design can be easily transferred to another design.
  • Child pages can often be nested several layers deep into the design

Top-Level Schematic Page

The top-level of our design shows 8 hierarchical blocks (the 9th, power, is not shown on this particular diagram).  Each block represents a child page.

The schematics for the Badge design are laid out in a hierarchical format out of necessity.  KiCad does not appear to have an option for a flat design.

Hard Way HughesWhen we started this course, we planned to use a flat-design, but KiCad seemed to require a hierarchical layout.  As the course has progressed, you've likely seen the schematic in both forms -- hierarchical in the online documentation I've created, and flat in Bob's original design files.  Future versions of this course will only show the hierarchical layout.