Industry Practices for Schematic Design?

Question

As my designs (and PCB designs too) become more complicated, I'm interested if there are best practices or industry standards for schematic design. I know there's a schematic checklist but I'm looking to go further with my designs. I've been following a simple design methodology based on signal inputs & outputs go left to right, with power flowing from top to bottom, which has worked well for simple schematics. Some of the questions I have thought about but can't find an answer:

• What's considered the maximum number of parts on a single page?
• What to consider when making a schematic multiple pages?
• When should I consider putting multiple tracks into a buss?
• How should I name busses, netlists, and the references to other pages?
• How should I place components to minimize the number of nets?
• What kind of comments should I include on a schematic?
• Where should I place the designation and value for horizontal and vertical components? Does it matter as long as I stay consistent?
• Should I note component packaging & rating on the schematic? Meaning discrete vs SMD or if a specific resistor is high powered?
• Should I customize nets in different colors or widths?
• How should I version control schematics?
• What workflow should a single person use to keep designs organized?

I'm sure there's more to consider on schematic design, this is just what I've run into with my own work. I'd appreciate additional topics on schematic design too.

Answer 1

What's considered the maximum number of parts on a single page?

Depends on the size of the page. You can fit more on a D-sized plotter sheet than a B-sized (roughly A4) sheet. Don't crowd things to the point it gets difficult to read.

What to consider when making a schematic multiple pages?

Almost all my designs end up as multiple sheets. Sometimes the manufacturing guys cut them all up and paste them together in one big plotter sheet to make it easier to follow the signal flow. But normally I don't print out bigger than 11x17 so I work at that size.

Something you didn't ask: I tend to make the first sheet be the critical input and output connections of my circuit, and work up towards more complex circuits on later pages. Other people like to put the critical signal path parts on the first page, and the input and output connections end up deep in the stack of schematics. I'm not sure which is really better.

When should I consider putting multiple tracks into a buss?

I rarely do this, but its a matter of style (and convention in your workgroup).

How should I name busses, netlists, and the references to other pages?

I tend toward all-caps net names, but otherwise I don't have fixed rules. More disciplined organizations might have more detailed rules.

How should I place components to minimize the number of nets?

I prefer to place components to make the signal flow clear. I don't worry about the number of named nets.

What kind of comments should I include on a schematic?

Anything important for the layout guy to know (matched length traces, place bypass caps near ICs, etc.) Anything a future engineer might need to know if they're looking to replace an obsolete part. Non-obvious critical specs like higher-than-normal resistor power requirements or tight tolerances. Anything that has to be tuned in production (Like "tune pot to achieve 50% duty cycle" or whatever).

Where should I place the designation and value for horizontal and vertical components? Does it matter as long as I stay consistent?

I use vertical text for vertical components to allow more parts to fit cleanly on a sheet. Others (apparently) consider this a grave sin. Be consistent and be consistent with others in your organization.

Should I note component packaging & rating on the schematic? Meaning discrete vs SMD or if a specific resistor is high powered?

Specifying the package type for each part visibly on the schematic would be clutter. But obviously that information has to be in the design to get transferred to layout. As mentioned above mention nonobvious specs that might trip someone up if they have to replace an obsolete part or find an alternate vendor due to a shortage.

Your BOM (Bill of Materials) will need to specify an exact manufacturers part number (or a list of acceptable alternates called an AVL "approved vendor list") for each part.

Should I customize nets in different colors or widths?

I don't recommend this. I'd prefer to get schematics that make sense if printed out in black & white.

How should I version control schematics?

I store datecoded backups (like "mydesign_20120205.zip" on my own pc and a remote share drive. Definitely store a backup whenever you release a design (either to layout or to manufacturing).

Edit: There are better ways to do this (see comments) but a simple process like dated zip files is also perfectly workable.

What workflow should a single person use to keep designs organized?

Keep backups. Use all the tools you have available. If you aren't doing your own layout, keep good communication with the layout guy.

Answer 2

For the version control, I use the same technique as with firmware.

Everything to do with a particular project gets put into one directory, with folders named e.g. "Firmware" "Hardware" "Documentation", etc. Then I use GIT with Assembla to commit/push any changes daily.
This means GIT takes care of all the tracking, I can go back to any point from the start of the project and does away with saving 20 different versions of something.

I have a standard backup that runs daily on my important folders too just in case.