Electrical Schematic Best Practices

As far as I know, there are no standard guidelines for drawing schematics. Most of us learn by trial-and-error, pick up the habits of our teachers, or just never learn. I think it’s time that these guidelines found a home.

The purpose of an electronics schematic is simple, to describe how components are electrically connected. A schematic does not necessarily indicate the physical relationship between components, though a good schematic will make this obvious when necessary.

The difference between a good schematic and a bad schematic is a matter of how easy it is to understand. If another person is able to look at the schematic and simply understand it, you have made a good schematic, if another person has to look at your schematic and decipher it, you have made a bad schematic. Here are my suggestions for making a good schematic.

Labels and Comments

Labels and comments on your schematic come at no cost to you so you might as well use them. You should always label your components. Most schematic editors will do this automatically for you, but if yours doesn’t then you must do this. There are some generally standard designators in use today, the most common are:

These rules are extremely helpful when sharing your designs with others, or when you need to come back to your design in the future. However, having correctly referenced parts is not necessarily enough to make a good schematic. It is also good practice to comment on non-standard parts or on important performance details.

For example, if you have a component that requires a very large power trace or special shielding then you should note this on the schematic. For more advanced circuits, such as RF designs, you would also want to note required trace lengths or impedances.

There are too many examples to list all of the situations in which you should make use of comments, but a good guideline is to ask yourself “If I were to look at this circuit in one year, would I still know what it is doing and how to take it to layout?” If it passes this test then you are on your way to creating a successful design.

Another recommendation for making your schematics clear is to be mindful of where your labels and comments are placed. If a label is placed over another label or over a component outline then you might as well not have it there at all because it won’t be readable. Take the few extra seconds to move your labels into a logical position near the component while not overlapping other components or labels.

The final guideline for proper labeling is to remember to label your most important nets. Don’t go overboard with this, but a few net names to remind you of functionality is an incredibly simple way to ensure that you are making an understandable schematic. Additionally, keep the names as short as is reasonable, use all caps, and separate words with underscores.

This means that instead of “Pin going to output” as a label you would want to do something like “TO_OUT” or even better, just “OUT.” This will ensure that you have readable schematics with signal names that are obvious and intuitive.

Good labeling practices vs. poor labeling
Good labeling practices vs. poor labeling

The Logical Schematic

I’m not certain where the convention came from, but it is always customary that inputs come from the left, outputs go to the right, power comes from the top, and ground or negative voltages go to the bottom. I recommend following this convention whenever it is possible and reasonable to do so.

Of course you can’t always do it, but at the very least try to separate your power pins from your I/O pins. If you have multiple voltage rails, the more positive voltages are generally higher on the schematic, though this is not a do-or-die rule.

An illogical circuit vs. the standard common emitter
An illogical circuit vs. the standard common emitter

Dot your i’s and cross your t’s. Well, something like that, this is a convention that comes from the days when low resolution photocopying was common. It is universally accepted that you should make a very clear dot where two wires form an intersection, your CAD package will usually handle this for you but it is good to keep in mind.

Related to crossing connections, you should also try to avoid 4-way connection points. This is another recommendation from the days of photocopying circuits, but it never hurts to design for longevity.

The proper way to connect three wires
The proper way to connect three wires

Using Hierarchy the Right Way

The final pointer in ensuring that your schematic makes sense is to utilize hierarchy effectively. This means that you separate logically different parts into a new sheet. By all means, if you can fit your entire design into a single sheet without cramping it together and still following the other rules, you should do that. Otherwise you might as well separate functionally different parts of the design into separate sheets.

There are different ways to do this in each CAD package, but the basic idea is the same. By keeping related components near each other and avoiding the clutter of other components you will be able to more easily verify and debug your design.

If your schematic doesn’t necessarily require multiple sheets then you should still do your best to attempt to introduce a bit of order into the chaos that is an electrical schematic. My preferred method is to draw a box around a functional unit and then place a label inside the box to indicate what that design does.

Demonstration of Functionally Separate Blocks
Demonstration of Functionally Separate Blocks

Other Tips

In addition to the general guidelines above, I have managed to compile some other tips that will lead to a successful design. If you have some of your own, feel free to submit them in the comments below (along with an explanation) and I will add them to the list.

Like I said, these are just a few tips I have picked up from my experience, if you have your own then submit them in the comments and I will add them to the article. Now that you know the best practices for getting your design into the computer, get to work! The next step is to start with the physical layout, this is where it starts to get interesting and you will want to have a solid schematic under your belt before you move on.