PCB Schematics Style Guide

As I work at the intersection of hardware and software, I spend a fair amount of time reading schematics for printed circuit boards (PCBs).  I’m astounded at how sloppy most schematics are, and have come up with a few suggestions to consider.

  1. Schematics are not only design entry — schematics are documentation.  Unless you are writing all the software, handling all the manufacturing, and debugging all field issues yourself, there will be others who will be using them.  Be considerate.
  2. Not everyone has a D size plotter (even B size printers are fairly rare).  I have a rather large (27″, 2560×1140) monitor, and have seen schematics that I have to zoom in to read.  Schematics should be created such that they can be printed on letter size paper (everyone has a letter size printer), and easily read — even by folks in their 60’s.  This is fairly simple — just spend some time breaking large symbols into smaller sections, and use a few more pages.  Even for viewing on a screen, putting less stuff on each page makes it easier to scroll through pages.  Most people print out schematics for review or bench work — so having letter size pages makes this possible.
  3. Schematics should be organized to have one function per page, or group similar functions on a page.  Don’t intermix power supplies and an audio codec unless they are related.  We realize the importance of organizing software in modules, and a large schematic is really no different.
  4. Keep all pages the same size.  When every page is a different size, you can’t easily scroll through pages, or print them out.
  5. Avoid hierarchical schematics.  For most PCB designs, hierarchical schematics offer no advantage over a flat schematic logically organized on pages.  PCB’s can only be so big, therefore even if you have 20 pages for a schematic, 20 pages is really not all that much, and adding hierarchy to 20 pages just adds complexity and makes them harder to read.  In a sense, your schematic page becomes a “hierarchical block.”
  6. Off page references are the key to making smaller schematic pages work.
  7. Spend a little more time putting a little art into your schematic symbols.  If you have a DB-9 connector, and you draw a connector in the shape of a DB-9 (only takes a few more minutes), then you can instantly recognize what it is in the schematic, and it is much quicker to find the circuit you are looking for during debugging sessions.  The same can be said for USB connectors, etc.  In some cases, it may make sense to draw a connector symbol to match how it looks physically, so you can quickly find a pin on the bench without digging out a datasheet.
  8. Schematic text must be easily searchable.  I don’t want to install a clunky schematic viewer that only runs on X.XX version of windows just to search for text.  I want to use the PDF reader I already have installed.  Make sure schematics are cleanly exported to PDF, and are easy to search.

I’m sure there are many other ideas — in a brief search, I turned up the following: