Scale Fields in Schematic Title Blocks - Page 1
Forum section: electronics / general

author: NF6X
author_rank: Unknown
timestamp: September 06, 2023, 05:27:28 pm
content: I am designing the title block templates for my drawings in Altium, though this post is not specific to Altium. I'm bringing up a new Altium-based flow at my new $DayJob, and trying to establish good drawing conventions for our PCB designs. I'm an Altium noob; I've previously used KiCad and PADS.Default schematic title blocks in various PCB layout tools commonly include a "Scale" field. The convention of specifying drawing scale makes sense to me for drawings of physical objects, but does it serve any useful purpose in electronic schematic diagrams for PCBs?I suppose I might include a scale field in my schematic diagrams just for consistency with title blocks in assembly drawings, etc. where physical scale is meaningful. The title blocks for various kinds of drawings in Altium are defined in different files, and they don't follow a consistent design in the example templates which come with AD23.It appears to me that I'll need to replicate the same title block many times for different sheet sizes, and for different drawing types, including editing them in at least two different tools. I'd like to get it all over with once before I start cranking out PCBs in Altium. My coworkers who will also design PCBs don't follow consistent drawing conventions, either from inexperience or just not caring. I'm trying to set a good example, and hopefully convince coworkers to use the templates I define.I'd like to see some opinions about best practices for the "scale" field in electronic schematic diagram title blocks, such as whether to include it at all and what to enter in it when physical scale is meaningless. I'd also welcome topic creep into considerations such as whether the convention of having a revision table on a drawing still makes sense when drawings are all electronic and stored in revision control systems. I have my own opinions about such things, but maybe my opinions could stand to be challenged by different perspectives.

author: Uky
author_rank: Regular Contributor
timestamp: September 06, 2023, 06:25:21 pm
content: It seems that many title blocks included with schematic tools are derived from mechanical standards.I never use "scale" but instead during first tool invocation, I modify all title blocks and insteadcreate a file "paper size". Later, when selecting a new design use that field for paper size if needed.The tool I use provides a set of title blocks that can be modified and have properties addedwhich can be automatically transfered to a corresponding title block for use in the PCB assembly drawingwhen finalizing a design project.For most designs, in Europe where I live, I use a drawing size of A3 (297 x 420 millimeter - landscape orientation)or even the larger A2 but only if an office paper printer can scale an A2 drawing to lesser size A3 without making the drawing to hard to read.Defining eg. A3 or A2 paper size results in when creating a .PDF in that size, that the aspects of the drawing elements(wire thickness, text readability, etc.) can be maintained. Later printing such a .PDF and selecting a smallerpaper size like A4 for an A3 .PDF print output will not affect drawing readability.A3 can in most cases be printed out by a standard home office printer that only handles A4 (210 x 297 mm) by shrinking it.Regarding revision information... I have over the years experienced a more or less continuous flow of engineering changesthat has to be included yesterday. Since revisioning is tedious even for a project that is still on the lab bench wherepaper print outs are likely to be all around the office, I created a field "Last modified" containing date and time thatgets automatically updated every time any one makes any sort of change to a schematic drawing (except printing.)Revisioning is still there but is used when releasing the design for fabrication. Some of my customers add an extra front page in a multi-pagedesign and uses that page for detailed descriptions of changes made for each major design revision that is made.In my system, separate revision information templates can be created and placed as non-components that does not appear in BOM or in netlists.Sorry for all metric references...

author: NF6X
author_rank: Unknown
timestamp: September 06, 2023, 07:18:56 pm
content: Thank you. I hope to see more anecdotes like yours. There is no need to apologize for using metric references.I also include a sheet size in my title blocks. Here in the US it's usually one of the ANSI sizes (A, B, C...) instead of the ISO sizes (A4, A3, A2...) since those are the common printer paper sizes sold here. I usually draw schematics on ANSI B size sheets (often called "Ledger" or "Tabloid"), which are similar to ISO A3 size. 99% of printers here print on ANSI A size, usually just called "Letter", and similar to ISO A4. Inkjet and laser printers which can handle the larger B size aren't too expensive or uncommon. I avoid using larger sizes like ANSI C or ISO A2. We have large format inkjet printers at work which can print them, but I find the larger sizes to be cumbersome in the post-drafting-table era.A last-modified field is a good idea, especially for changes in between releases. I plan to include a similar field, as well as a git revision field. I still have to decide how I will handle the revision field in the main title block. I think the manufacturing folks at my company like to see letter revisions like "A" or "B", but I like to distinguish between PCB layout revisions vs. component value changes on the same PCB layout. I've previously used a dotted numeric convention like X.Y, where X is the PCB layout version and Y is the BOM revision. But I don't think that would be accepted as well in my new job.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 07, 2023, 03:07:17 pm
content: Scale does not make much sense for the schematic.In KiCad, there is no scale field in the default page layout, but as it uses the same page layout for both the schematic and PCB, maybe there would be some reason to add it. But who ever draws a PCB to something other than a 1:1 scale?(Some eagle users did this to get around the 100x100mm artificial limit of the free version of that program).

author: NF6X
author_rank: Unknown
timestamp: September 07, 2023, 03:11:50 pm
content: Good point about the scale naturally being 1:1 in anything KiCad produces. I'm not far enough along in Altium yet to be sure, but I have the impression that the drafting tool in it may allow things like assembly drawings to be made at other scales?

author: Uky
author_rank: Regular Contributor
timestamp: September 09, 2023, 07:34:49 am
content: PCB's are in most cases never designed in any other scale than 1:1 but documentation like assembly drawings with dimensions is another thing. I have had customers with designs like 14 x 30 mm, containing microprocessors and RF circuitry using component sizes 0402 or even 0201. If the tool used can upsize the assembly drawing without at the same time scale the title blocks it's OK. The tool I use can create assembly details in larger scale and retain the PCB gerber in its original size while still having all this information including drill drawing, drill table, cross section view and dimensions in one single file.