Noobish question - how do I exclude components from a PCB?

Don't put them there.

That's an obvious workaround. What if I do want to put them there. They contain valuable information after all - grounding, rating of the fuse, DPDT-ness of the switch, wire colors of the transformer's windings. Can't I use the same schematic for PCB and assembly?

It just occured to me that I probably wasn't clear enough on what I want to accomplish. I don't want to exclude them from the schematic per se. Just from the PCB. In other words, I'm trying to find a way to mark some of the components as "don't even bother placing pads for these".

Put them in a separate schematic?

Leon

This problem occurs all the time with any CAD tool. You need to create your symbol in such a way that it is only a schematic symbol and it doesn't "forward" to the PCB, but still shows up on the BOM. I don't know how to do this in OrCAD. The problem in reverse is test pads, they show up on the schematic, thus are a "part", but are not purchased, they are pads on the PCB, so they aren't on the BOM. Maybe if you look around the documentation for test points, it will show you the properties you need to play with.

Create new PCB componment shapes that will appear as patterns of holes on your PCB. Link these shapes to the schematic symbols.

You will need to place through-hole pads for these, as otherwise it will not be easy to run the wires from those parts to the PCB.

I'd forgotten this, but the Pulsonix software I use lets me create schematic only parts. These may be added to a schematic and won't appear on the PCB. They actually appear on the parts list, which is useful.

You might be able to do something similar.

Leon

A CAD system I used long ago allowed you to put a "no-op" parameter on a schematic part that you didn't want on the board.

Failing that option, a couple of solutions come to mind:

1. Draw two schematics - one with the switch, fuse, and transformer and any other off-board parts, and a box to represent the board. The second schematic would show only the parts on the board.

1. Draw the whole thing as one schematic, and just ignore the off-board components when laying out the board - you will get DRC errors, but they can be ignored. You might want to initially place the off-board components on the PCB layout (but outside the board boundary) so that the "update PCB from schematic" function won't keep placing them on the board as you work. You can delete the off-board parts before creating the Gerbers.

Just use Tango to make the PCB layout, and you can place things however you like... ALL by hand. A power supply isn't so complicated that you would even need checking routines at all.

I have always done choice (1). It makes it much easier to separate the board assembly task from the system assembly task, as you can make each of these tasks boil down to "make these here electronics match that there schematic".

Service personnel may not see the 'system view' as easily, but at least they won't be wondering what's on the board and what isn't.

Are you using a particular CAD or board layout program? That will drive the details on how to do what you want.

If its a human being interpreting the schematic, all you need to do is to enclose the parts of the schematic that will be mounted on the board with a decent looking border. In addition, you should use appropriate symbols for the connections to the board. People are pretty good at figuring these things out (unless you get a moron to build your boards).

I don't understand. Why not create a schematic without the parts you don't want. Then create the PCB from that schematic.. and if all goes well add to the original schematic the parts that are not going to go on the pcb.

shortT

With the gEDA flow, what you'd do is create one page for each pcb or harness, using off-page connection "symbols" that can be mapped to whatever holes/connector/whatever you'll be using to connect the boards together. For example, I have a symbol for "left pin" and "right pin" which map to "hole" on the pcb, so I can have two left pins on the left side of the schematic page for (in my case) the AC lines from the transformer, and map them to holes to solder wires to on the pcb. On a *separate* schematic page, you have the wiring for the switch, fuse, transformer, etc. When you do the schematic->pcb flow, you simply exclude the harness page. When you do the schematic->BOM flow, you include both pages.

Not sure how this maps to OrCAD though.

Optimally, one would have a tool (CAD) that would allow the creation and maintenance of a single system schematic which has an assembly or board view. One attribute of each component would be the assembly, subassembly, or board to which it belongs.

For manufacturing purposes, assembly views could be generated tailored to the task at hand. For design, simulation, and maintenance, system-wide schematics, netlists, etc. can be generated.

Back in my days at the lazy B, one of the primary contributors to wiring configuration errors was the practice of maintaining multiple views of each system in separate CAD systems. Even with "perfect" import/export functions (and none were really perfect), the time delay involved in propagating a design change through the system would almost guarantee that aircraft were being built to multiple versions of the engineering data.