Hi Philip,

> Anticipating that I might have a little time to get started on the 
> node board over the weekend, I had a few questions.

That's great! Let me through up some requirements tonight.

> If this is the type of thing I should just post to the avionics 
> list...

Totally. I've CC'd the list.

> * Everything is in metric


> * I use IPC-7351B land patterns for standard parts. Typically, I use 
> the "nominal" condition patterns, but I wonder if "most" might be the
> better choice here to be more robust mechanically

We think nominal is best: that's what we've used, and have had no
problems so far. The problem with "most" is that it really gets in the
way of tight layout sometimes.

* I label part values like 3k3 (3.3kohm) or 4u7 (4.7uF) to avoid
overlooked decimal
> points

We use decimals because that's what most people are used to. So I'd
recommend you use them, although it's not a big deal either way.

> * I prefer that schematic symbols represent the physical devices

So this is getting into religious warfare territory, but we really
prefer schematic symbols. "package schematics" create twisted, weird
schematics that are hard to understand. We really like being able to
show data and power flow through "intuitive" layout - things tend to
flow left to right, things are visually connected, etc.

Also, it's 2013, so moving back and forth between schematic and board
level should be easy when you're debugging.

> * I use standard US symbols...

Yes, please. Except for EAGLE's standard "US" capacitor symbol is
polarized, which is the stupidest thing ever. So we use the European cap
symbols, and American everything else.

> * Looks like you prefer to have parts libraries specific to each 
> project. If not, are there some standard libraries?

In avionics-cad/libraries, you'll find a giant mess of libraries. We
really need to clean that up, maybe we'll do that over the next week.

We do tend to do one library per part or family of parts. That's mostly
because EAGLE's part libraries are broken, and hard to merge. I haven't
tried to merge the new XML lbiraries, maybe we should try that? But I
guess yes, for now, let's continue that separate library idea.

> * There seems to be a preference for drawing busses and wired
> connections vs. connection by name.

For the love all that is holy, yes. I admit that this again religious
intolerance, but using just labels for nets is a terrible crime against
humanity. I say this because schematics should be *visual* displays of
data/power flow. You shouldn't have to hunt across a giant schematic
for the same net. Yes, you can automate this, but being able to glance
at the schematic and see the connection is just so much better.

And when you can't do this, then we like to use "off sheet" connector
symbols, to warn you it's going somewhere else.

Hmmm, why isn't this written up like this somewhere? OK, I'll put that
on my plate to do as well. :)


Andrew Greenberg

Portland State Aerospace Society (http://psas.pdx.edu/)
and...@psas.pdx.edu  C: 503.708.7711

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