[PCB_FORUM] Re: Metric to English - English to Metric
- From: "Schwartz, Jerome" <jschwa01@xxxxxxxxxx>
- To: <icu-pcb-forum@xxxxxxxxxxxxx>
- Date: Tue, 30 Aug 2005 12:31:14 -0400
I have considered designing in metric only for a while. It would
make
routing cleaner in BGA's etc. I have two reasons for not using metric.
These
might only be unique to me.
1. My designs can only be fabricated in the US. All of our vendors will
convert
the metric Gerber data to English. Thereby, creating the round off,
and offset, problem
I wanted to avoid in the first place.
2. Grade school, in the 1960's, tried to teach us metric. It still
hasn't taken. "You can't
teach an old dog new tricks." Therefore, I would always be
converting in my head.
IMHO (In My Humble Opinion) Although I am am seldom humble ;)
Regards,
Jerry Schwartz, CID+
IPC Advanced Certified Designer
"May The Schwartz Be With You."
Designer 3
Harris Corporation GCSD Voice (321)-727-5474
P.O. Box 37, MS 1-11F Pager (321)-690-9797
Melbourne, FL 32902-0037
mailto:Jerome.Schwartz@xxxxxxxxxx <mailto:Jerome.Schwartz@xxxxxxxxxx>
http://www.harris.com <http://www.harris.com/>
NOTE: IF SOMETHING I SAY CAN BE TAKEN TWO WAYS AND ONE OF THEM OFFENDS
YOU. I MEANT THE OTHER ONE.
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Gene Carman
Sent: Tuesday, August 30, 2005 12:05 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to English - English to Metric
You guys are doing layouts in copper right? What kind of
tolerance do you think you get anyway?
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of
george.h.patrick@xxxxxxxxxxxxxx
Sent: Tuesday, August 30, 2005 8:33 AM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to English - English to
Metric
Whatever you say, Austin. PADS changed mathematics so
there would be no round off.
--
George Patrick
Tektronix, Inc.
Central Engineering, PCB Design Group
P.O. Box 500, M/S 39-512
Beaverton, OR 97077-0001
Phone: 503-627-5272 Fax: 503-627-5587
http://www.tektronix.com <http://www.tektronix.com/>
http://www.pcb-designer.com <http://www.pcb-designer.com/>
It's my opinion, not Tektronix'
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Austin Franklin
Sent: Monday, August 29, 2005 19:45
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to English -
English to Metric
George,
I'm not sure what reason you are referring to
here, but from what I can see, there is only one real reason and that is
because there is a problem with Allegro. If this problem was fixed,
there would be no reason not to switch back and forth. It really isn't
magic. People do it in PADS (and other programs) all the time.
Regards,
Austin
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of
george.h.patrick@xxxxxxxxxxxxxx
Sent: Thursday, August 25, 2005 6:35 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to English -
English to Metric
All the more reason to...
( wait for it ... )
Stay in the same units you start with!
(K.I.S.S) :))
--
George Patrick
Tektronix, Inc.
Central Engineering, PCB Design Group
P.O. Box 500, M/S 39-512
Beaverton, OR 97077-0001
Phone: 503-627-5272 Fax:
503-627-5587
http://www.tektronix.com
<http://www.tektronix.com/> http://www.pcb-designer.com
<http://www.pcb-designer.com/>
It's my opinion, not Tektronix'
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of richard moffat
Sent: Thursday, August 25, 2005 15:20
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to
English - English to Metric
Sorry - I wrote a " when I shoulda put
mils. Same maths and numbers apply.
>>> annoonan@xxxxxxxxx 26/08/2005
10:14:23 a.m. >>>
Hi Richard,
I think we talked about using 2 decimal
places in MILS, not inches. Again, I haven't taken any time to go
through the motions yet myself.
I can see though, how 2 decimal places
in INCHES would cause undesirable results.
Regards,
Andrew
________________________________
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of richard moffat
Sent: Thursday, August 25, 2005 3:08 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to
English - English to Metric
This will work most of the time,
sometimes it will trip you up. eg:
0.0009mm -> 0.0354"
0.0354" rounds to 0.04"
0.04" -> 0.001016mm
0.001016mm rounds to 0.001mm
so you see you've lost some accuracy
already. Caveat emptor ...
>>> annoonan@xxxxxxxxx 26/08/2005
3:56:24 a.m. >>>
Hi Kanak,
Someone made an interesting suggestion
yesterday. When you must switch back and forth, set the accuracy in
millimeters to 4 decimal places, and the mils to 2 decimal places.
Apparently this removes the rounding errors. I haven't tried it my self,
but it's worth a try if you need to use this approach.
Andrew
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Kanakaraj
Sent: Wednesday, August 24, 2005 9:11 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to
English - English to Metric
Hi,
In my project, the customer has given
the mechanical dimensions of the connectors and mouting holes in mm. (
with three digit accuracy like 21.213 mm). I place the connector with
milimeter as measurement unit and switch back to mils for routing.
When we are doing the dimensioning, we
again switch back to milimeter, then we encounter errors upto two
decimal points. ( the connector fixed at 21.213mm is showing as 21.192
mm.. for an example).
have any one encountered issues like
this? how can this be fixed.
Regards
~Kanak
----- Original Message -----
From: george.h.patrick@xxxxxxxxxxxxxx
To: icu-pcb-forum@xxxxxxxxxxxxx
Sent: Thursday, August 25, 2005 3:39 AM
Subject: [PCB_FORUM] Re: Metric to
English - English to Metric
The question remains:
WHY switch back and forth?
If the board is started in one unit, you
are making it harder on yourself and others switching back and forth,
even with NO round off errors. The grids are different, the trace
widths are different (unless you LIKE typing two decimal places all the
time). It is senseless to be switching it around, unless it is just to
make extra work for yourself or your international partner. Why not
just KEEP IT SIMPLE (K.I.S.S.) :)
--
George Patrick
Tektronix, Inc.
Central Engineering, PCB Design Group
P.O. Box 500, M/S 39-512
Beaverton, OR 97077-0001
Phone: 503-627-5272 Fax:
503-627-5587
http://www.tektronix.com
<http://www.tektronix.com/> http://www.pcb-designer.com
<http://www.pcb-designer.com/>
It's my opinion, not Tektronix'
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Patrick Jabbaz
Sent: Wednesday, August 24, 2005 14:58
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to
English - English to Metric
Here is the trick to make it work, In
Allegro,
You can switch units from metric to
mils, and vise versa without errors, if you have the following setup:
User Units mils use 2 decimal places
User Units millimeter use 4 decimal
places
Using this process, allows you to switch
back and forth without any round off errors.
Patrick Jabbaz
Sr. PCB Design Eng.
Xilinx
2100 Logic Drive
San Jose, Ca 95124
Direct: 408-879-4709
M: 408-621-6533
email: patrick.jabbaz@xxxxxxxxxx
________________________________
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Austin Franklin
Sent: Wednesday, August 24, 2005 2:26 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to
English - English to Metric
Hi Richard,
Perhaps more than a decade ago, the CPU
and code speed may have been an issue. But, in the realm we are talking
about (a printed circuit board and the range of numbers and precision
necessary) IMO and IME the compiler imposes no significant restrictions,
nor does the "math processor" in the CPU. Again, it is simply a matter
of knowing where the decimal point is.
In Allegro, you don't convert because
the tool can not handle it. In a tool that can adequately handle it,
this is not an issue.
Regards,
Austin
-----Original Message-----
From: icu-pcb-forum-bounce@xxxxxxxxxxxxx
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx]On Behalf Of richard moffat
Sent: Wednesday, August 24, 2005 5:15 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Metric to
English - English to Metric
Cadence is probably making a compromise
for speed. The way that other tools may allow a seemless interchange is
to have a greater length of significant numbers in the internal
database, especially converting metric->imperial.
The programmers are restricted to that
they are given: The C compiler, and the maths processor on the CPU.
In short: don't convert!
>>> austin@xxxxxxxxxxxx 25/08/2005
9:08:15 a.m. >>>
Hi,
> Conversely, 1/10 (0.1) cannot be
exactly represented in base 2...
I design ASICs, and I have done a LOT of
arithmetic functions in ASICs, and
use decimal points all the time. All
hardware arithmetic functions are done
in base 2. It's simply a matter of
knowing where the decimal point is and
using enough digits. Yet, it goes on to
explain the solution (as I said,
knowing where the decimal point is)...so
I fail to see the *real* problem.
As was pointed out, PADS has no problem
switching back and forth between the
two unit systems, so I simply don't
believe Allegro can't do it as well. It
seems like this may be a self imposed
restriction:
> The real issue is that some numbers
can't be represented exactly in the
> standard floating point
representation.
Why do they have to use "standard"
floating point representation anyway?
Sounds like someone programmed
themselves into a corner, and instead fixing
it, they are trying to come up with
explanations...instead of solutions.
Sigh. To me, this is a huge weakness of
Allegro.
Regards,
Austin
________________________________
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