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Schematic drawing conventions

T

Tom Wells

Am I the only one who finds the current practice of straight crossed lines (with dots signifying a connection) to be lazy
and poor draftsman practice?

I recently had to debug a control circuit where the manufacturer didn't even use dots, making the circuit totally ambiguous,
requiring that I make disconnections and trace wires to verify the actual intended circuit.

They have crossed lines on 3-ph 480 circuits ( which aren't connections ) and crossed lines in 24v AC control circuits,
which WERE connections... Well, which IS IT, Mister?

If I have to guess, I wonder how you got out of engineering school,

I give an "F" to this lazy, sloppy effort.

Suppose I'm just a fossil, but this really honks me off.
These people wouldn't have made it out of the school I went to. :mad:
 
Tom Wells said:
Am I the only one who finds the current practice of straight crossed lines (with dots signifying a connection) to be lazy
and poor draftsman practice?

I recently had to debug a control circuit where the manufacturer didn't even use dots, making the circuit totally ambiguous,
requiring that I make disconnections and trace wires to verify the actual intended circuit.

They have crossed lines on 3-ph 480 circuits ( which aren't connections ) and crossed lines in 24v AC control circuits,
which WERE connections... Well, which IS IT, Mister?

If I have to guess, I wonder how you got out of engineering school,

I give an "F" to this lazy, sloppy effort.

Suppose I'm just a fossil, but this really honks me off.
These people wouldn't have made it out of the school I went to. :mad:
Click to expand...

Tom, in case you haven't noticed, there ain't no draftsmen no more! ;)

I prefer the little semi-circle in the vertical wire's path where wires cross, to indicate no connection. That's the way I have always done with my hand-drawn schematics.

But I haven't hand-drawn a schematic in many moons, as doing it with a computer is a real time-saver. CAD drawings are easier to modify (to correct or to amend), to export to PCB layout programs, and easier to distribute, store and print multiple copies.

However, you are then left to the mercy of the CAD program's standard, which usually is crossed lines with a dot indicating a connection, and no dot indicating no connection. :(

That being said, as useful as it would be for every engineer to use the same symbols, and the ARE symbol drawing standards (IEEE, etc.), once you recognize the way the engineer or CAD program drew things in a particular drawing, you SHOULD be able to be confident it will be the same elsewhere within that drawing. With hand-drawn skizzes, well, it's up to the dilligence of the draftsman...and one would hope that associated drawings and revisions are made using the same standard, one way to avoid questionable situations as you describe.

David Reaves

PS:
When I first started using a computer to draw schematics, I used MacDraw Pro and created my own symbols. Now I use Designworks, because it has relatively advanced database-linking features, etc. But I still think my old MacDraw symbols looked neater. ;-)
 
We were issued RCA xmittting tube manuals and receiver type manuals at school and advised that our schematics
should ideally look like these. Jump-over lines to make sure a dot was not intended.
Sam's Photofacts were drawn to the same convention.

The worst is when resistors are mere rectangles.
Another annoyance is ambiguous or incorrect use of the earth-ground symbol where chassis ground is clearly intended.
 
I was taught to use the 'loop over' convention to indicate wires which pass but are not joined, and a dot
to indicate an electrical connection.
I still use this today when I hand draw a schematic (which I have to do from time to time when I find a PCB
that doesn't come with a manual).

Another issue relating to this is files output by PCB CAD drawing programs.

I spent the best part of a day last week drawing up a schematic and producing a neat and tidy board layout
using Eagle CAD Pro, only to find that my usual board maker doesn't accept Gerber files!

He wants .pcb files and they seem to be produced using Protel software which I don't have. GRRRRR.
 
Okay, so which schematic software has provision to do jump overs and jagged lines for resistors?

Wait...Let me guess. None?
 
You would think that some programmer would have figured out how to do this. Perhaps it would be best programmed by someone dedicated to solving this. It doesn't seem that it would be any harder to design a scaled pixel by pixel resistor icon or loop over icon than any other character.
 
Gave up trying to make the half-circle for non-connections, but use a solid dot for connection. That works OK for me.

Started using the poor man's AutoCAD “Generic CAD” back in the 90s'. Not really made to do schematics but they already had some components in their library. Made my own components that I still use today. I did have to go to a Generic CAD clone "General Cadd" when I moved to Windows 98. Uses the same command structure and works just like to the GenericCAD with some nice enhancements. Does fine with W7.
 
It would be trivial for a skilled programmer to create a version of SPICE that allows for this, since the original SPICE was created at Berkeley and is therefore under the Berkeley Software Distribution license. This allows anyone to make changes and distribute the result freely.

When I draw a schematic by hand (which is rare), I draw proper resistors and use jump over wires. But like everyone else said, the computerization of schematic drawing has led to "final" computer-printed schematics using the "nothing means nothing, dot means connection" standard.

I suspect this is by design. When circuits get large, the semicircle hops can get in the way. Look at the schematic for a micro-controlled robot. (For example: http://www.convergencepromotions.com/atmelonline/v_8/pdf/atmeljournalnewsletterrobot.pdf, see page 3) This particular circuit has very few "hops" due to good design, but look at the 7 segment display at the bottom center. Would it be more or less readable with the semicircles?
 
Tom Wells said:
Okay, so which schematic software has provision to do jump overs and jagged lines for resistors?

Wait...Let me guess. None?
Click to expand...

Microsoft's Visio does jump-overs and jagged lines for resistors. I've been using it for years - quite happy with it, actually.
-D
 
The 7-segment display would, I feel be more readable with jump-overs. In '81, when microprocessors were pretty much just the
Z-80, and the 8080, we were required to draw out complete schematics of working designs, with complete lines for data bus, address bus, and clocking, etc, no "implied" lines, and with jump overs.

I'll have to look at the Visio software, and some of what it can do.

When I submitted formal drawings for my patents, I was shocked at what passed for acceptable drawings,
and did "proper" bristol board and india ink drawings. I first asked my father, an accomplished draftsman and
machinist, what he thought. When he said they were good enough, I knew there'd be no rejections from the USPTO.
This aspect worried even more than the inventing or writing the specification.
 
I prefer the jumpovers, but I can take the dot - no dot convention. I can't take the crossed lines which may or may not connect (connection selection determined by circuit parameters?). I'm not a fan of squares with little numbers which get confused with littler uF symbols, and everything's a square. Visio gets it real close, use that if you're too lazy to draw it.
 
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