Re: gEDA-user: New Column: From the CAD Library
On 2/7/2011 11:21 AM, Peter C.J. Clifton wrote: On Feb 7 2011, rickman wrote: The real question is does the current method cause any problems? When this was discussed a few months ago the answer was no. So why worry about 1 part in a million error? Engineering is all about tolerances. We do have some problems with rounding and 45-degree lines, but I'm not convinced metric units internally is a magic bullet for that. Display of accurate coordinate in metric IS a problem though. How so? I thought the dimensions in these tools are done with 10 microinch resolution. Isn't that enough for anything on the visible horizon? Actually, I wouldn't think the display is the problem, but rather the problem would be generation of rounded data for output such as Gerber files. What are people using this software for that requires better than 10 millionths of an inch accuracy? Rick ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: New Column: From the CAD Library
What are people using this software for that requires better than 10 millionths of an inch accuracy? The problem people see is that a metric grid is rounded to the inch units, so a 45 degree line does NOT always end on a grid point, due to X and Y being rounded different ways. So PCB adds an 0.01 mil stub on the end to connect the diagonal line to the grid point. ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: New Column: From the CAD Library
On Mon, 07 Feb 2011 13:30:24 -0500 rickman gnuarm.g...@arius.com wrote: On 2/7/2011 11:21 AM, Peter C.J. Clifton wrote: On Feb 7 2011, rickman wrote: The real question is does the current method cause any problems? When this was discussed a few months ago the answer was no. So why worry about 1 part in a million error? Engineering is all about tolerances. We do have some problems with rounding and 45-degree lines, but I'm not convinced metric units internally is a magic bullet for that. Display of accurate coordinate in metric IS a problem though. How so? I thought the dimensions in these tools are done with 10 microinch resolution. Isn't that enough for anything on the visible horizon? Actually, I wouldn't think the display is the problem, but rather the problem would be generation of rounded data for output such as Gerber files. What are people using this software for that requires better than 10 millionths of an inch accuracy? I often see some odd values due to inexact conversion to millimeters in pcb. It slows me down when I'm trying to draw a footprint since I have to constantly round the numbers in my head; while easy, you have to be constantly doing this every time you click a point and it is a waste of time. See a simple example on the screen shot: http://gibibit.com/upload/2011-02-07_pcb_mm_error_display.png. Here I used the measure tool to measure a distance between two points on a 0.5 mm grid, but the displayed result is not correct. Sure, mathematically it is extremely close to the correct value, but for my brain to convert this each time I glance at the position/measurement display in pcb, it does accumulate since I refer to the display so frequently. Regards, Colin ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: New Column: From the CAD Library
On Mon, 7 Feb 2011 13:38:30 -0500 DJ Delorie d...@delorie.com wrote: What are people using this software for that requires better than 10 millionths of an inch accuracy? The problem people see is that a metric grid is rounded to the inch units, so a 45 degree line does NOT always end on a grid point, due to X and Y being rounded different ways. So PCB adds an 0.01 mil stub on the end to connect the diagonal line to the grid point. So that's why I get the little stubs... That is actually a more annoying problem than the length display error since those stray stubs clutter the layout, especially when you want to select and delete/move/modifiy groups of traces. Regards, Colin ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: New Column: From the CAD Library
Hi all, -Original Message- From: geda-user-boun...@moria.seul.org [mailto:geda-user-boun...@moria.seul.org] On Behalf Of Peter Clifton Sent: Saturday, February 05, 2011 3:49 PM To: gEDA user mailing list Subject: Re: gEDA-user: New Column: From the CAD Library On Fri, 2011-02-04 at 08:17 -0500, Bob Paddock wrote: New Column: From the CAD Library When creating a CAD library, there are dozens of things to consider that are often overlooked or not even considered that will directly affect the quality of part placement, via fanout, trace routing, post processing, fabrication, and assembly processes. This article, Part 1 of a series, introduces aspects that should be considered when creating CAD library parts. http://www.pcbdesign007.com/pages/zone.cgi?a=74214 Has tips worth considering. Note that the series continues on his blog. It is VERY good, and contains a lot of details I was looking for recently. http://blogs.mentor.com/tom-hausherr/ -- Peter Clifton Electrical Engineering Division, Engineering Department, University of Cambridge, 9, JJ Thomson Avenue, Cambridge CB3 0FA Tel: +44 (0)7729 980173 - (No signal in the lab!) Tel: +44 (0)1223 748328 - (Shared lab phone, ask for me) +1 I've been following Tom Hausherr's achievements (the formerly PCB-Libaries, now Mentor Graphics) for a couple of years now, and I think that this blog is mandatory reading before Getting Started with pcb design. I would like to see some, if not all, of these standards reflected in the pcb-lib some day _and_ these recommendations end up in the (gEDA) pcb documentation, just to prevent error 404 from happening. Of course, there are others sources of information to read before putting the first trace on a pcb, like app notes and part datasheets from vendors. One of Tom's issues that is to be kept in pcb are most of the mil grids because of the bazillion perf board and mil based parts on the market, to be bought for cheap by hobby-ists, or for Quick-and-Neat proto boards (we don't play or do dirty ;-). Just my opinion on the subject. Kind regards, Bert Timmerman. ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: New Column: From the CAD Library
Bert Timmerman wrote: I would like to see some, if not all, of these standards reflected in the pcb-lib some day _and_ these recommendations end up in the (gEDA) pcb documentation, just to prevent error 404 from happening. copy-paste would require that he releases the text under GPL, or compatible. One of Tom's issues that is to be kept in pcb are most of the mil grids because of the bazillion perf board and mil based parts on the market, to be bought for cheap by hobby-ists, or for Quick-and-Neat proto boards. ack. But the role of mil and mm should be exchanged. The file format should be metric at the bottom. Imperial measures should be derived on the fly. ---)kaimartin(--- -- Kai-Martin Knaak Email: k...@familieknaak.de Öffentlicher PGP-Schlüssel: http://pool.sks-keyservers.net:11371/pks/lookup?search=0x6C0B9F53 ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: New Column: From the CAD Library
On Sun, 2011-02-06 at 10:55 +0100, Bert Timmerman wrote: One of Tom's issues that is to be kept in pcb are most of the mil grids because of the bazillion perf board and mil based parts on the market, to be bought for cheap by hobby-ists, or for Quick-and-Neat proto boards (we don't play or do dirty ;-). Just my opinion on the subject. Imperial parts are not a problem for a sufficiently fine metric grid. I don't think we should remove the option of working on a Mil grid though. I do it most of the time, even though I realise it is a habit best got out of. Way forward: Metric nm grid internally, parts defined in whatever units the vendor's controlling dimensions are in. This might require relative origins to be used between the part design coordinate and the board's snap-grid, but that seems to be mandated by various IPC standards anyway. -- Peter Clifton Electrical Engineering Division, Engineering Department, University of Cambridge, 9, JJ Thomson Avenue, Cambridge CB3 0FA Tel: +44 (0)7729 980173 - (No signal in the lab!) Tel: +44 (0)1223 748328 - (Shared lab phone, ask for me) signature.asc Description: This is a digitally signed message part ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: New Column: From the CAD Library
On 02/06/2011 09:24 AM, Peter Clifton wrote: Imperial parts are not a problem for a sufficiently fine metric grid. +1 I heard Tom Hausherr talk last year about grids, land pattern generators. For his suggestion to just go metric, it works with old inch spaced protoboard layouts just fine if enough resolution is used. It's always going to be valuable to combine the old with the new, where you might have very fine line spacings in the new on a metric grid, the base drawing being a metric grid, and placing the inch stuff on a calculated-from-metric semi inch grid only means some holes are off by 0.025mm or less if using a 0.05mm grid. Meanwhile, any scripted tool we can write to help make parameterized footprints from datasheets will be one of the biggest aids to pcb layout. Much of our discussion about ways to vote on or log successful uses of footprints in production of boards seems invalidated by the industry adoption of most nominal and least density styles of footprints where the IPC specifies extension of pad area beyond a part lead in mm. The manufacturer's suggested footprint is pretty much ignored by such a standard, yet deriving footprints from lead shapes for 2 terminal chips and gull wing leaded parts is what the usual commercial tools (and thus the usual commercial layout folks) do. When it comes to chip scale packages I didn't see any suggestion to change the MFRs land pattern. Hausherr does suggest BGAs get the three density levels, but the denser ones are only used on throw away products. IPC recommendations seem to take BGA shapes as published by MFRs and make them a little larger for robustness. The writeup on http://blogs.mentor.com/tom-hausherr goes over the same material I heard in person last year about fairways between microvias put in BGA ball lands planned for many tracks in inner layers of 8 and up layer boards used for dense products these days. Figure 20 and 21 are for board layouts, but look like chip layouts of the 1990's! Blind buried microvias here we come? John -- Ecosensory Austin TX ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: New Column: From the CAD Library
On 2/6/2011 10:24 AM, Peter Clifton wrote: On Sun, 2011-02-06 at 10:55 +0100, Bert Timmerman wrote: One of Tom's issues that is to be kept in pcb are most of the mil grids because of the bazillion perf board and mil based parts on the market, to be bought for cheap by hobby-ists, or for Quick-and-Neat proto boards (we don't play or do dirty ;-). Just my opinion on the subject. Imperial parts are not a problem for a sufficiently fine metric grid. I don't think we should remove the option of working on a Mil grid though. I do it most of the time, even though I realise it is a habit best got out of. I don't think you understand the intent. I don't think anyone is suggesting any changes to what a user sees. The issue is what base units are used internally and in libraries. By using metric values, imperial (is that really the right term?) measures (aka inches and mils) can be represented and calculated with no loss of precision. However, when inch type units are used as the fundamental measurement, it can be harder to get adequate precision to represent metric units. 1 inch = 25.4 mm... exactly 100 mm = 3.937007874016... sort of. In reality if you use enough precision in the base units you can always get close enough which is what engineering is about. But some folks have an issue with not working in the best possible manner. I'm not sure this is really an issue. There would be significant pain making the change now. If the change is to be made at a later time, will it really be any more painful? So if there is no significant reason to switch and the pain does not increase if delayed... why bother with it now...? Way forward: Metric nm grid internally, parts defined in whatever units the vendor's controlling dimensions are in. This might require relative origins to be used between the part design coordinate and the board's snap-grid, but that seems to be mandated by various IPC standards anyway. Parts should match the rest of a system I think. The dimensions of a part can be stored in the units that best suit the system. It seems silly to store a part as metric and let the system round it off to inches on the fly rather than to do the round off when the part is created. But that's just my opinion. Rick ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: New Column: From the CAD Library
On Sun, 2011-02-06 at 12:27 -0500, rickman wrote: Parts should match the rest of a system I think. The dimensions of a part can be stored in the units that best suit the system. It seems silly to store a part as metric and let the system round it off to inches on the fly rather than to do the round off when the part is created. But that's just my opinion. Conversely, to me it seems silly to deliberately loose information on the part's original specification. If the manufacturer specifies some dimension as 1mm, that is how it should stay represented in our source design files, not 39.3700787 mils (or however one chooses to round it). PCB already supports reading units like 1mm in its input files, but it always saves out the rounded imperial representation. Sure - it probably doesn't matter if you round everything based on true position when creating the file, but if the user were to copy+paste part of that new (rounded) footprint using an imperial grid, to make a longer part - rounding errors could easily be compounded. -- Peter Clifton Electrical Engineering Division, Engineering Department, University of Cambridge, 9, JJ Thomson Avenue, Cambridge CB3 0FA Tel: +44 (0)7729 980173 - (No signal in the lab!) Tel: +44 (0)1223 748328 - (Shared lab phone, ask for me) signature.asc Description: This is a digitally signed message part ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: New Column: From the CAD Library
Am 06.02.2011 um 16:24 schrieb Peter Clifton: Imperial parts are not a problem for a sufficiently fine metric grid. I don't think we should remove the option of working on a Mil grid though. I'm wondering what's the advantage of having an internal grid at all. Why not just use doubles, describing a position in meter or millimeter? About all mechanical CAD and picture drawing applications do it that way. Markus - - - - - - - - - - - - - - - - - - - Dipl. Ing. (FH) Markus Hitter http://www.jump-ing.de/ ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
Re: gEDA-user: New Column: From the CAD Library
On Fri, 2011-02-04 at 08:17 -0500, Bob Paddock wrote: New Column: From the CAD Library When creating a CAD library, there are dozens of things to consider that are often overlooked or not even considered that will directly affect the quality of part placement, via fanout, trace routing, post processing, fabrication, and assembly processes. This article, Part 1 of a series, introduces aspects that should be considered when creating CAD library parts. http://www.pcbdesign007.com/pages/zone.cgi?a=74214 Has tips worth considering. Note that the series continues on his blog. It is VERY good, and contains a lot of details I was looking for recently. http://blogs.mentor.com/tom-hausherr/ -- Peter Clifton Electrical Engineering Division, Engineering Department, University of Cambridge, 9, JJ Thomson Avenue, Cambridge CB3 0FA Tel: +44 (0)7729 980173 - (No signal in the lab!) Tel: +44 (0)1223 748328 - (Shared lab phone, ask for me) signature.asc Description: This is a digitally signed message part ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
gEDA-user: New Column: From the CAD Library
New Column: From the CAD Library When creating a CAD library, there are dozens of things to consider that are often overlooked or not even considered that will directly affect the quality of part placement, via fanout, trace routing, post processing, fabrication, and assembly processes. This article, Part 1 of a series, introduces aspects that should be considered when creating CAD library parts. http://www.pcbdesign007.com/pages/zone.cgi?a=74214 Has tips worth considering. ___ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
