I hereby certify that I am not simply asking someone else to design a footprint for me.
What is the best way to create and maintain one schematic, with two different PCB layouts - one for THT and one for SMT?
I could simply copy the whole project, but I would prefer to have a way to maintain the common data. This is non-trivial because most parts will have different names and footprints, but not all - some connectors or TO220 devices used on SMT board are the same, Some have the same value but different footprints (resistors).
Someone must have solved this problem already, and I ahve other wheels to reinvent!
The differences between SMT and THT are pretty big. Apart from the obvious (Different footprints, different PCB area needed) routing of the footprints will also be different. You can put lots of tracks under an THT resistor, but not so much for an SMT resistor for example.
I guess there is not much interest in this in general. Sure, projects are reworked (most often from THT → SMT) but that is mostly a one-off, and after that the old version gets archived, and therefore I’m not so sure whether this has already been “solved”.
You could make a setup in which different projects (because of different PCB’s) link to the same schematic files, but that still leaves de problem of different footprint assignment for THT / SMT. Maybe it’s possible to do this with “variants”, or else it could be done by modifying the schematic by swapping out footprint info. For example, each symbol could have a “footprint_smt” and an “footprint_tht” field, and then the script copies one or the other to the normal “footprint” field.
Scripting is slowly coming to the schematic editor. In KiCad V8 you can open a python console in the schematic editor, but I have no idea if there is an interface behind it to do much with the schematic. But KiCad’s file formats are text based, and a script for such a substitution could be easily written with an external command line script.
I believe you have already asked yourself a basic question: Do I really need it?
It would be interesting the answer to this question as it is hard to imagine for me where from is such need.
I think it is going to depend on a couple of factors:
the complexity of the circuit
the density (or lack of) of the layout and spare space on the PCB
If the design is not very complex and you have space to spare on the PCB you can dual footprint, i.e. have THT and SMD footprints for each component on your PCB and route tracks to both.
You would obviously have to do the same on your schematic.
This question has been asked before, IIRC several times, and some solutions (workarounds) have been offered, but I don’t remember if anyone gave an example project. This one is one possible solution. As was said, KiCad doesn’t support two PCBs from one schematic “natively”, but if you insist, it’s possible.
You can put all your stuff in a schematic sheet and duplicate the sheet. Afterwards you should rename it’s filename so the sheets don’t share the same file.
Than you can assign unique footprints to each sheet. With the populate option you can unpopulate all stuff from one of the two sheets. Than place the stuff from the other sheet and make a board out of it.
When you are finished, rename the board file and start over, but this time you populate the other sheet’s components.
However applying updates may become tricky with this method.
What I would do:
You can also use the 2 sheets and simply make both boards in the same board file. Afterwards you can use the pcb editor in standalone mode. And copy paste one of the 2 boards to a new file.
The new board files aren’t attached to a schematic. If you need to do an update, you can do so in the double board file, than copy past again to the other board files, replacing their content entirely.
I think this may be the least cumbersome method. Having that said, duplicating the entire project is propably even easier.
And than there is the brilliant idea of JMK
If the design is not very complex and you have space to spare on the PCB you can dual footprint, i.e. have THT and SMD footprints for each component on your PCB and route tracks to both.
In this design I put an SMD resistors underneath the the THT resistor. I also used an optocoupler which has similar footprints in DIP and SMD (SM DIP). I simply duplicated every symbol in the schematic and made 1 normal board out of them.
So people are free to solder THT, SMD or let JLCPCB assemble it for them.
Did you try my example project? Updates to the schematic work naturally and automatically. No copying, no swapping files, no scripts, no editing text files or anything like that.
Out of all this, NOMB but I am curious as to the reason for the OP request. My hands have never been so steady, and during the 1990s I was intimidated by the thought of working with SMT. Of course I have not completely purged through hole from my designs but I cannot imagine going back to all through hole. I cannot think of any advantage given the fact that you are designing a pcb.
Is the OP willing to share the reason for wanting to hang on to all through hole?
I am the original poster. The reason was that I teach electronics, and wanted the THT version as teaching tool and possibly a student project. The students are unlikely to be great with SMT parts. It might also be of interest to the wider YouTube audience as a home project.
Also, I prefer to experiment with THT. This is partly because I am old and my eyesight is not very good.
Meanwhile the SMT version was to be a saleable product. As this would be machine assembled, SMT is fine,
I will, as had been suggested, split the project. In reality, maintaining the different sets of components is definitely
better documented by having different drawings than having a spreadsheet with different mappings, or trying to maintain a PostgreSQL database of the the alternative options :-{. Its not that complicated (less than 50 components).
I’m now a few years over 50 and eyesight is also going down. A few years back I bought a stereo microscope (Amscope or clone with a big head), and with it soldering small SMT parts is now easier then soldering THT parts has ever been.
For students It would be nice to compare the size difference between the SMT and THT versions. There can be performance differences because SMT parts have lower parasitic properties then THT parts. There is also a huge difference i how small you go with SMT parts. The bigger versions are quite easy, even without a microscope, while the smallest will still be very difficult to hand dolser even with a microscope. for resistors, 0805 size is easy, most people with sharp eye sight find 0603 also quite doable, but going smaller and it starts becoming ever more difficult. See:
SOT-23 is a very common package for active parts and is easy to hand solder. SOT-23 -6 is the same size, but significantly more difficult to solder because it has 6 connections in the same package.
There are also “solder challenge” PCB’s. Usually they have a bunch of blinking LED’s in ever smaller size.
I am 72. I just got some new eyeglasses, but only somewhat adjusted from whatever I got before.
I get two eyeglass prescriptions. Both are bifocal. One is for normal use (such as driving and reading) and the other is for “close and closer.” This latter one has a dividing line between the two lens portions. I do not fully understand the meaning but I have posted a screenshot of my “close and closer” eyeglass prescription in case that might be helpful. Anyway, I find this to be adequate for almost all of my SMT work. If I need to examine something more closely I use an illuminated desktop magnifier. But I seldom use that.
I got into electronics (via amateur radio) when I was 13. I inherited unsteady hands from my father, and that used to drive me nuts when I started out. Assembling a kit it might take me an hour to do some delicate assembly portion which would have required 2 minutes with good skilled hands.
Nowadays my hands are no worse than when I was 13. I think I am generally more relaxed about it; that helps. If I expect to do some delicate SMT work, I try to have a beer before I start. That helps a lot!!
BTW: It took me a moment to realize that @paulvdh image of 0201s appears to be with the chips on someone’s finger. If that is not small enough, there is also such a thing as 01005 chip size. In spite of my relatively unsteady hands, I routinely work with 0603s and I find that most colleagues do not like to work with smaller (such as 0402) by hand. I also prefer to avoid 0402s but I can do them occasionally if I need to and if I have at least 1-2 spares for every one I need to solder. I would not attempt 0201s.
I am 75. I built an audio amp at 13, an oscilloscope at 14 and pirate radio station at about the same age - we did spoof news bulletin that JFK had been assassinated 2 weeks before he was! I also debugged valve based digital counters (with some help from a friend a year older). In the summer holiday, I built the first 1,000 Sinclair X10s (or maybe X20s).
I am still doing SMPSes, and have done industrial motor control up to 1MW which saved up to 30% on electricity bills
that were probably very big indeed (1MW 24/7 ???).
My glasses prescriptions are probably quite similar to yours - two pairs (near and close-up), both varifocal, and I also have some (older) driving glasses which I only need for night driving. I have a desktop spot-light as well for close up. I find the magnifier is useless - but I have used better ones at work in the past - I suspect they cost a lot of money.
I too would not use 0402 or anything smaller. Not sure if I could tell a 01005 from a spec of dust!
I use SMT for production designs, but I don’t see how you could expect people with no previous experience to start with SMT - it helps enormously to have visible differences between resistors and the various capacitor technologies.
And SMT Connectors? for 10A? or 600V? I don’t think so!
I am currently working on a more efficient EV power system - based on work I have done previously (eg industrial motor control) - I expect to extend range by about 15%.
My hands are still quite steady, but I get tired easily.
I don’t know anything about the quality of these things, as I already mentioned I bought a stereo microscope myself. The dustcap on these desktop magnifier can be kind of important, With a bit of bad luck these things can become a fire hazard if direct sunlight comes from just the wrong angle.
You are not kidding! I used to have a round glass paperweight on my desk like this. I came home from work one day and I found a large scorch mark on my desk next to a pile of paper. Sadly the paperweight now has to live in a drawer…
