Left-to-right schematic flow with combined I/O connector

[chostetler]

Good morning,

I had a question about schematic layout guidelines. I am aware of the general guidance that signals should "flow" from left to right, have high voltages up and low voltages/ground down, etc. But what do you do if you have a connector with both input and output wires?

Say I have a circuit that has one input, three outputs, Vin, and GND that all enter/exit the circuit through the same connector J1. Physically, where should I place J1 on the schematic? It has both intputs and outputs, so there's no obvious position for it. I can think of a couple options:

• Put J1 on the left, and simply loop the outputs back around with a net. Or vice versa, with J1 on the right.
• Use net labels for whichever connections are on the "wrong" side - so if I put J1 on the right side of the schematic, then create an net label for the input signal.
• Use net labels for every connection, and hide the J1 symbol down in the corner of the schematic
• Split up the pins of J1 into individual symbols that can be placed wherever needed

I can think of advantages and disadvantages to each of these. Personally, I prefer to avoid labels, so I would probably do option 2, likely placing J1 on the left side. Do you have a preference for which way is the "best" way to do it?

[Benta]

There's no "one size fits all" answer to this one.

Personally, I usually go with a "majority decision".
I your case, you have three outputs and two supply lines that all belong on the right. And one input that belongs on the left. So the connector goes on the right side. This principle eases routing the wires and gives better readability.
Another option is placing connector top or bottom of the sheet.

Whether you connect the input using wire or labels is more a question of your style. I'm not a big fan of labels, but when they're needed I tend to place a text label next to it pointing to the sheet coordinates where its counterpart is to be found.

[Siwastaja]

Don't overthink it. This is where your let your intuition, or taste, decide.

Such rules are not absolute anyway, actually deciding the edge/corner based on direction of the signal is totally arbitrary one and pretty weird one; one that is clearly wrong and only makes sense in some limited cases by accident. It makes much more sense to group the signals based on purpose, for example in a motor controller board, you might have SPI on the left because it communicates with a microcontroller, and say motor control outputs and current measurement inputs on the right. Having MOSI, SCK and NSS and motor current measurements on the left, and MISO and motor control signals on the right on a motor controller would be weird as fuck.

You can apply the idea of the flow direction, though - is the IO controller more for controlling or getting status? Maybe that could be a deciding factor. But if it's both, then it really doesn't matter where you put it.

[chostetler]

Don't overthink it. This is where your let your intuition, or taste, decide.

I figured as much. Thanks for the confirmation  .

[tggzzz]

Don't overthink it. This is where your let your intuition, or taste, decide.

I figured as much. Thanks for the confirmation  .

Good taste is key, but what constitutes good/bad taste?

For me the starting point point is whatever makes the schematic readable and understandable.

[EPAIII]

I have seen and had to work with several systems for handling this situation and, as others have said, three is no single answer.

I have seen equipment that had dozens and dozens of PCBs or modules, each with one or more connectors. The schematic for one PCB or module could cover a fold-out page or even two or three of them. Not only did the draftsman have to handle the IN/OUT connectors but also net labels to carry the signal from page to page. It helped a lot to have a good sense of organization: not just left to right, but also top to bottom in many cases. Such drawings seemed to work best if IN/OUT connector(s) were placed in a standard position on all the PCB or module schematics. Or, it was easy to understand what was happening if a connector that carried both IN and OUT connections was broken up into two halves, one on the extreme left of the first page and the other on the extreme right of the last. And signals that went to somewhere in the middle were carried across with complete lines (except for jumping from one page to the next). Just label them both as J1 and show dotted lines up to an S curve to indicate the break on each half. This would be on the bottom of the left half and the top of the right half. If three segments are needed then the middle one would have the break indication on both top and bottom. It kind of shows the flow.

But that's an extreme example. It may have been just my bad luck to meet with it so many times.

If your schematic fits on one page, then I would say there would be no harm in placing half of the combined signal connector on the left and the other half on the right. Again just label them both as J1 and show dotted lines up to an S curve to indicate the break on each half. That would be my choice. Oh, and you don't need to get pictorial about all this. That may be OK for connectors with a small number of pins, but when there are dozens and dozens of them, just simple blocks with numbers in them are better. I am working on a device with a DA-15 connector and I did choose to draw the pins in their actual pattern. That is about as many as I would do that with. I am hoping it will help with the circuit board layout where I intend to use strip board. It's a one-off.

Your numbers:

2. So you would have the connector surrounded by regular lines for connections on one side and net labels on the other. I don't like that.

3. Net labels for every connection? So almost none of the connections would be made with a full line? Definitely not. I have had to work with drawings like this: they stink! This would make understanding the circuit almost impossible. The very idea of a schematic, unlike a pictorial of the device, is to make the operation of the circuit EASY to understand. Or, at least as easy as possible. Don't take it in the opposite direction.

4. The connector pins all over the drawing? Not just no, but HELL NO! Worse than #3.

That's my take on it and I have seen an awful amount of schematics. Had to work with them and figure out what was going on. Make it easier, not harder.


PS: This is a great question for a beginner to be asking. This is the beginner forum, isn't it. Stuff like this should be taught BEFORE Ohm's law.

[tggzzz]

3. Net labels for every connection? So almost none of the connections would be made with a full line? Definitely not. I have had to work with drawings like this: they stink! This would make understanding the circuit almost impossible. The very idea of a schematic, unlike a pictorial of the device, is to make the operation of the circuit EASY to understand. Or, at least as easy as possible. Don't take it in the opposite direction.

Agreed.  In spades. Avoid like the plague.

Dubious advantage: it does make it clear the circuit is designed by someone more familiar with software and a keyboard than electronics.

PS: This is a great question for a beginner to be asking. This is the beginner forum, isn't it. Stuff like this should be taught BEFORE Ohm's law.

Agreed, again - with the caveat that good taste is very difficult to teach. Grok the subject (any subject) and good taste will be the natural consequence

[tooki]

Good morning,

I had a question about schematic layout guidelines. I am aware of the general guidance that signals should "flow" from left to right, have high voltages up and low voltages/ground down, etc. But what do you do if you have a connector with both input and output wires?

Say I have a circuit that has one input, three outputs, Vin, and GND that all enter/exit the circuit through the same connector J1. Physically, where should I place J1 on the schematic? It has both intputs and outputs, so there's no obvious position for it. I can think of a couple options:

• Put J1 on the left, and simply loop the outputs back around with a net. Or vice versa, with J1 on the right.
• Use net labels for whichever connections are on the "wrong" side - so if I put J1 on the right side of the schematic, then create an net label for the input signal.
• Use net labels for every connection, and hide the J1 symbol down in the corner of the schematic
• Split up the pins of J1 into individual symbols that can be placed wherever needed

I can think of advantages and disadvantages to each of these. Personally, I prefer to avoid labels, so I would probably do option 2, likely placing J1 on the left side. Do you have a preference for which way is the "best" way to do it?

I completely agree with everyone who says “it depends”, but I’ll also add another option (which might be what you intended with #3, but not with how others interpreted #3):
5. Use net labels for all the connections in the connector only, placing the J1 symbol down in the corner. Net labels feed signals into the left side of the circuit and send them out the right side.

[Sagar]

Left to right reading is just for good readability and reproduceability, so that in case of troubleshooting everything is cleared. So you can arrange the connector accoriding to that, if you want to use nets use them, want lables use them. Just we need a connection. Btw, if you want to be specific then place it with majority i.e right.