Schematic preferences [Design]

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From: D Yuniskis on 19 Jan 2010 03:29

John Larkin wrote:
> On Mon, 18 Jan 2010 18:39:06 -0800 (PST), MooseFET
> <kensmith(a)rahul.net> wrote:
>
>
>> The reference of a part encodes the page it is on. R307 is on page 3
>
> Yikes! Production would lynch us. After the layout is done, we
> resequence the reference designators in physical and numeric order and
> back-annotate the schematic.

Ditto. The problem I find with EDA tools is they don't let you
put "tags" in text on the sheets. E.g., if you have a note:
"D1 - D4 installed on heatsink" and you backannotate the
schematic, D1 may no longer be D1, etc. So, you have to manually
go through and update the notes. It would be nice if you could
set up cross reference tags like in DTP tools...

From: mpm on 19 Jan 2010 08:26

On Jan 18, 3:37 pm, D Yuniskis <not.going.to...(a)seen.com> wrote:
> Hi,
>
> Of course, this is *highly* subjective -- but, I'd enjoy hearing
> folks' "conventions" used when preparing schematics (that *others*
> will consume -- how you scribble for your own purposes isn't
> important as it depends a lot on what *you* want out of the
> drawing).

My main rule (a preference actually) is that the same name be used in
the callouts when a circuit involves several schematic sheets!

I once worked for a video company that had a PLL circuit that
traversed 6 or 7 different circuit boards.
I guess each engineer / designer was responsible for his own board,
because none of the names matched up.
This made final device test & calibration very difficult.

This device comprised roughly 75 "D-size" sheets of schematics.
I can still smell the ammonia from the Diazit copier..

From: MooseFET on 19 Jan 2010 09:20

On Jan 18, 7:02 pm, John Larkin
<jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote:
> On Mon, 18 Jan 2010 18:39:06 -0800 (PST), MooseFET
>
> <kensm...(a)rahul.net> wrote:
> >The reference of a part encodes the page it is on. R307 is on page 3
>
> Yikes! Production would lynch us. After the layout is done, we
> resequence the reference designators in physical and numeric order and
> back-annotate the schematic.

We haven't done that since the 1980s. The technicians were the ones
that
suggested the change. We used to do boards with things like RA12
meaning
column A row 12.

From: MooseFET on 19 Jan 2010 09:22

On Jan 19, 12:29 am, D Yuniskis <not.going.to...(a)seen.com> wrote:
> John Larkin wrote:
> > On Mon, 18 Jan 2010 18:39:06 -0800 (PST), MooseFET
> > <kensm...(a)rahul.net> wrote:
>
> >> The reference of a part encodes the page it is on. R307 is on page 3
>
> > Yikes! Production would lynch us. After the layout is done, we
> > resequence the reference designators in physical and numeric order and
> > back-annotate the schematic.
>
> Ditto. The problem I find with EDA tools is they don't let you
> put "tags" in text on the sheets. E.g., if you have a note:
> "D1 - D4 installed on heatsink" and you backannotate the
> schematic, D1 may no longer be D1, etc. So, you have to manually
> go through and update the notes. It would be nice if you could
> set up cross reference tags like in DTP tools...

For issues like that:
Put "NOTE 1" next to the parts on the heat sink with a dashed outline
Then make NOTE 1 say "These parts are on the heat sink"

From: MooseFET on 19 Jan 2010 09:39

On Jan 18, 8:16 pm, krw <k...(a)att.bizzzzzzzzzzz> wrote:
> On Mon, 18 Jan 2010 18:39:06 -0800 (PST), MooseFET
>
> <kensm...(a)rahul.net> wrote:
>
> <snip>
>
> >All parts have the power pins shown. The + is usually on the
> >top. The exception is references and regulators where it is
> >on the left.
>
> What about gates? All subcircuits get power pins? What about dual
> op-amps?

One of the parts of the op-amp show the power pins as does one logic
gate.

>
> <snip>
>
> >I never crossed lines as a connection point. If two lines connect
> >to another line, they are offset.
>
> Again, that uses a additional "wiring channel" on the sheet. Dots
> work fine.

Dots have lead to errors. If the reproduction of the schematic is
less than perfect a mere fly spec can send the technician down a
blind alley.

[... ground symbols ...]

What do you use for chassis ground?

>
> is a digital grounds. I know, they analog and digital grounds
> _should_ be the same. They will be soon. ;-)

You mean you don't flaot all your logic on the +5V plane?

------
-----! 7805 !--------+--------- Logic Vcc
------
!
+----------------------- Logic grounds
!
/---/ 5.1V
!
+----------------------- HC4051 Vee connections
GND

I really did do this and the technicians didn't even kill me
for it. I avoided adding a switching device to make a minus
supply for the Vee and the minus swings.

> >Mounting holes are shown if they have electrical meaning.
>
> Shields?

Shields are soldered to "mounting holes" and schematically show
as a dashed line running through the hole and around the area.

> >Notes go in the lower left corner of the sheet.
>
> We put general notes where they fit and specific circuit notes
> pointing to the device or circuit they're describing.
>
> >The reference of a part encodes the page it is on. R307 is on page 3
>
> We do that, sorta. Identical channels are numbered R1xx, R2xx,...
> Rnxx, no matter what page they're on. In one schematic four channels
> are on pages 3-7, but are still labeled R1xx for channel 1.
>
> I also like Larkin's reference numbering from side to side with the
> schematic being back-annotated after layout. That really helps debug.