Tips/Standards for creating electrical schematics?

Other Hardware General Electronics
1

I've been able to create a bunch of projects with various Arduinos, and since they've all been stand-alone projects, I've never needed to create a schematic. I've just been throwing parts together that I know work by themselves, and tinkering with them to work together in various ways. Now, I've got to move forward and start documenting these things.

I've seen several software recommendations for beginners and more advanced tinkerers for creating electrical schematics, and I've seen lots of posts on creating schematics, but none of them really discuss the tips that will make your schematic as close to universally understood as we can get. Therefore, my problem is that when I sit down to one of these applications, I don't know where to start, and I'm afraid I'll finish one of these things in a way that makes sense to me, but not to anyone else. Is there a guide/tutorial/list of tips anywhere that could give me some insight into the following:

  • A good order in which to draw the schematic (i.e., start with the microcontroller, move to X, then to Y, finish with Z)
  • Any conventions about common components (i.e., should there be only one 'ground' symbol, or can I throw around as many 'grounds' as I need to make it easy to read?
  • Any conventions about where to position parts on the page (i.e., do voltage regulators always go in the upper-right corner, or something like that?
  • Any conventions about how the traces are drawn? (i.e., anything like 'never have more than 2 joints in a trace', or 'never use anything but right angles'?)
  • Any other conventions that I haven't mentioned.

I'd like to have a little idea of what I'm doing before diving in, but then again, maybe diving in would be the best way to learn. Any suggestions would be greatly appreciated. Thanks!

2

Most schematic tools let you use a symbol for a connection to a supply rail (like Gnd or Vcc). I think in eagle this is the included "supply" library, or something like that. Use these. Point the Gnd symbol down and positive voltage supply rail symbols up.

Avoid non-connected traces crossing as much as possible - yes, you can see that they're not connected, but it is still much easier to get confused.

Put some effort into keeping traces neat - as you design a board, it's very easy to just connect things, and let the schematic get hideous.

Set the value of passives on the schematic.

3

Great tips, thanks! Any rules about where to put things, or can you just put anything anywhere, as long as it's easy to read? When should I break out smaller, simpler pieces from the larger picture and join them with a label (i.e., J5->J5)?

4

I try and set all inputs on one side and the outputs on the other so there is a flow from left to right or right to left

5

Another good tip. Is this a common convention, or a personal preference? Or are schematics much more free-form than I'm thinking at this point?

6

Study how other schematics are made:

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7

Another a good tip, larryd, thanks!

Also, what a difference a word makes. I've been searching over and over with the phrase "how to create an electrical schematic," and all I've been getting is how to create a circuit from a schematic. I just searched for "how to draw an electrical schematic" and I got some great results. Here are a few:

These all have a bunch of tips, guidelines, and best practices like I was looking for. Thanks to those here for the starter tips!

8

Also, see Sparkfun's discussion:

https://learn.sparkfun.com/tutorials/how-to-read-a-schematic

9

A good order in which to draw the schematic (i.e., start with the microcontroller, move to X, then to Y, finish with Z)

Not so much the order, but arrange things in functional groups as much as possible. The microcontroller and supporting circuitry in one spot, voltage regulating circuitry in another, sensor and amplification/conditioning circuitry in another, etc.

Any conventions about common components (i.e., should there be only one 'ground' symbol, or can I throw around as many 'grounds' as I need to make it easy to read?

The entire point of having a special GND symbol is so that you can use it more than once and it is understood that they are all electrically connected, even though there is no wire explicitly connecting them on the schematic. The same thing is often done for the power rails. Many things have to be connected to power and GND, and often in very distant parts of the circuit. Connecting them all together with explicit lines just adds clutter instead of clarity.

The primary goal of a schematic is understanding.

Another trick that can be done to reduce clutter is to merge multiple traces together into a single "bus" trace. SDA and SCL for I2C almost always go together, so there isn't much point in drawing the two of them separately.

Any conventions about where to position parts on the page (i.e., do voltage regulators always go in the upper-right corner, or something like that?

Generally, higher voltages are positioned towards the top of the page, and lower voltages towards the bottom. Also, do not make your IC blocks a mirror of their pinout. Rearrange the pin arrangement into something that makes logical sense for your schematic.

Any other conventions that I haven't mentioned.

larryd's post has one. Judicious use of "broken" traces like in his schematic can prevent a bird's nest of intertwined traces, or prevent one long trace from snaking from on corner of your schematic all the way to the other and making it ugly.

It is important that both sides of the "broken" trace be labelled with a name so that you know which ones are connected to which.

10

Using broken traces works well when there are multiples of the same circuit. Picture the difference between drawing 5 leds with resistors connected to 5 different I/O pins, and one that has the led circuit drawn separate and the I/O pins only having a LED tag. As long as the circuit is the same, it is fine and can clarify the schematic, but as soon as you change a resistor for a particular Vf, a new circuit should be drawn.

Try to think logically. The schematic should read from left to right, and top to bottom as much as possible. Having something read like a maze just gets confusing

11

Draw the impotant parts of the schematic by hand a few times to sort out what
layout is clearest - make any symmetries in the circuit symmetrical in the diagram too
if possible.
This is particularly relevant for analog sections where common patterns re-occur such as
differential amps and cascodes and push-pull sections.

And there are two reasons to draw schematics, for design and for construction. The former
can just be a sketch of the important elements omitting support circuitry, the latter needs
all the details filled in and is worth doing in CAD so you can convert to board layout and generate
a BOM.

12

Hi,
Essential habit to acquire is as when you program, backup, backup, backup as you develop your schematic.

Add numeric suffixes to your filenames so your back ups are not over written and you have a chronological record of your developing schematic.
such as

mycircuit_1
mycircuit_2
etc

This means if you make a big stuff up, and I guarantee we all do at times when putting it all on paper, you can go back to just before the stuffup and rescue your project.

Tom... :slight_smile: