I’m creating a multi-stage low pass filter & attenuator.
I want to make TWO versions: low power, using SMD 0805 [or smaller] footprints, and higher power using through-hole components [5W resistors]. Same schematic, different footprints.
Is it possible to have both versions within a single project?
Yes you can. The method I would use is IAW the standard on applying reference designators, namely ANSI/ASME Y14.44 “Reference Designations for Electrical and Electronics Parts and Equipment”. The short of it is to use the non-class letter N (from IEEE 315, Clause 22.4) as a ref des prefix as follows: Assign N1 for your SMT parts and N2 for the THT parts. Thus you would have N1C1, N1L1, N1R1, etc. for your SMT parts and N2C1, N2L1, N2R1, etc. for your THT parts.
If you want further information on reference designations see the following:
Reference Designation of Electronic Parts
For the latest on reference designation of electronic parts see my blog posts at <www.txplore.com/blog>. Dr. Peter Dalmaris has kindly posted my seven articles on his Tech Explorations website out of Sydney, Australia. There is a main article and six appendices listed as follows:
(7) “Reference Designations For Electrical And Electronics Parts And Equipment”
Lawrence Joy
18 September, 2018
(1) “Appendix A. List of Pertinent Applicable Standards”
Lawrence Joy
20 September, 2018
(6) “Appendix B. Class Designation Letters”
Lawrence Joy
20 September, 2018
(5) “Appendix C: List of Nonconforming Class Letters”
Lawrence Joy
20 September, 2018
(4) “Appendix D. System Subdivision”
Lawrence Joy
20 September, 2018
(3) “Appendix E: KiCad Anomalous Handling of Suffix Letters”
Lawrence Joy
20 September, 2018
(2) “Appendix F: Scenario Questions and Answers”
Lawrence Joy
20 September, 2018
You should look at the main article , Nr 7, first and then the appendices. The reason the numbering is out of sequence is because the newer dated material is first, followed by the older dated material, and in order of posting. As you go down through the blog postings you will run across Appendix A first followed by Appendices F, E, D, C, and B. The main article “Reference Designations…” is last.
–Larry
I’m am not certain, but I don’t think there is a program supported method.
The main issue that I see is that there does not seem to be any easy way to generate the individual Gerbers for each separate board layout.
You didn’t specify if you wanted two separate PCBs or two PCBs made from the same board, only that you wanted the two circuits on the same schematic. If you wanted to lay out two PCBs on the same board you would use mouse bites or the V-groove method to separate them with the parts reference designated IAW the N# ref des prefixes as I wrote before.
If you want two separate PCBs the process is a little bit more involved. First do the schematic with the N# ref des prefixes. Then copy this overall schematic to two other schematics. This means there will be two other *.pro files. On the schematic for the SMT parts delete all the parts with N2 ref des prefix and then delete the N1 ref des prefix from the SMT parts. This will leave you with basic reference designators on the SMT board. On the second schematic delete all the ref des prefix N1 parts and then delete the N2 ref des prefix from the THT parts. This will leave you with basic reference designators for the THT board.
Did you want two PCBs from a single board or did you want two separate PCBs?
–Larry
Larry,
I’m looking to make 2 different PCBs for the one schematic. Mainly a low power SMD [0805 etc resistors are rated for 1/8 Watt] and a higher power PTH version [using 5W or 10W resistors].
I mentioned filters in the original question because -
Careful arrangement of pads in series / parallel will allow the SMD version to ALSO be used as a multi-stage passive filter [replace resistors with ceramic chip caps & inductors]
Thanks!
Combined with your other answer, I now have both a technique and several references to read.
Why can you use schematic hierarchy to include the same schematic into two difference projects (2 .pro files). From there you basically use the same schematic for difference layout.
The issue that I’m seeing here is the footprints are assigned from within the schematic. So once you load the same schematic file up in a second project and start changing footprints, the changes will also be reflected in the first project (because it is the same file). There might be something that can be done with different .cmp files, but I haven’t really used them so I could be mistaken.
Or, for this specific application come up with special footprints for all your components that can take both the small SMT and the larger wattage (THT?) parts.
I think I have a clearer picture of what you want to accomplish. You don’t want two PCBs, you want a single PCB layout that can accommodate SMT (surface mount technology) parts or THT (thru hole technology) parts or possibly a combination.
I have seen layouts for a PCB where there was provision for a packaged crystal oscillator in either an SMT package or a THT package. In this case the schematic diagram had two crystal oscillators reference designated with Y1 and Y2 (KiCad, or any other program, would prevent you from assigning the same ref des to two different parts). The land pattern/footprint was custom in that it was a combination of the SMT footprint and the THT footprint, one over the other and cross connected as required (the pin outs could have been different) but, of course, only one part would be used at a time. This will mess up the ERC but you would be aware. The parts list (PL) would have to be provisioned with “or” (either use Y1 or Y2) or there might be two PLs, a -1 PL and a -2 PL, where the one PL would call out the use of Y1 and the other PL would call out the use of Y2.
Now for your situation. I would do a schematic diagram using the class letter E (meaning miscellaneous electrical part) for each part. So, you would have E1, E2, E3, Etc. The graphic symbol would be generic, your choice but I would use either a square or rectangle. The footprint for each of these parts would depend on how you are going to mount the thru hole parts. Are you going to solder the leads of the through hole parts to the SMT pads or are you going to put plated through holes in the SMT pads? In either case your footprints are probably going to be custom. On the same drawing (*.sch) draw a second schematic with proper class letters and symbols for the circuitry you want in the same schematic locations as the E# ref des parts, but assign no footprints. You can repeat this as many times as you want for whatever configuration you want.
–Larry
I think the OP really does want two different boards
Besides which - putting alternative footprints for 10W components (maybe 50mm long) on the same pcb as 0805 is unlikely to be either a cost effective or good, functional solution.
There was this recent article on the forum - I have not tried it and I am not clear if it will address your particular use case but it might be worth some further investigation.
If that doesn’t work, in the end, it may simply be easier to copy the schematic into two separate projects.
Thank you.
I must admit, I’m tempted to make custom SMD pads, to allow use of 1218 size [1W rating] and 0805 [1/8 W rating]. That would give more options when building to lower power limits.
You are right about component dimensions for high power, and there’s another reason to keep it as a separate design: upper frequency response. The pads needed for PTH parts start to act as stubs when the frequency climbs, keeping them out of the SMD version should improve the frequency range.
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