Automatic route procedure

Excuse me for my naive question but I’m a bit lost about automatic auto route.
I’m using KiCad for my project and it’s very good cad. I need to develop an analogic
circuit and, net by net, I did it very well. Now, for digital nets, I’d like to use the automatic route because the critical analog net are done. But I don’t understand what I have to do to lunch the automatic procedure.
Can someone give me a suggestion please ?
I’m using the version 5.1.2.

Thanks a lot.

There is no autorouter available directly in Kicad. In the past there was a very rudimentary autorouter but that was removed before the 5.x series. Additionally there used to be a big yellow button which automatically linked to start a session with a free autorouter called Freerouting ( which you may see referred to in older documentation.

Freerouting is still available and there are (outdated) instructions on the Freerouting website about how to use it with KiCad. There are also a variety of Freerouting spin-off projects around - all of which with variable support However, to cut a long story short, there are some problems with the legal status and maintainace and support for Freerouting and some usability issues with Java apps in general. The developers did not want to build in obsolescence so removed the big yellow button and hence the direct support for Freerouting. However, the same functionality is available if you choose “Export DSN”, process the file in Freerouting and then import the session file.

Opinions are divided about autorouters - they have a role but are certainly not ‘just press a button and its all done’. There was a good talk at KiCon recently about this subject and how to use them most effectively.

What KiCad does offer is generally considered a more useful feature - a push and shove, interactive router.
This video gives you much more of an idea rather than try to explain it.


That’s just it, I’m looking at that still and I don’t see MOSTLY orthogonal tracks (each direction primarily on its own layer) joined by vias where the direction changes which take advantage of the paths between pads that you get when using through-hole devices. (Truth to tell my old tool had a fairly complex set of options where the designer got to select which algorithms needed to be selected that would be enabled for this session.) I stated on a previous response that the last time I used my previous tool to route a PCB it completed its job (and passed DRC) in all of 2 seconds. The primary reason I’m leaving that tool is Microsoft no longer provides support for the OS it was primarily designed to run on. If a router which runs that quickly and does its job that thoroughly is to be regarded as “obsolete and worthless” I certainly do not agree, and any tool worth its salt certainly ought to allow its users to continue to take advantage of any inherent advantages that certain methods of parts placement happen to provide. If FreeRouting doesn’t provide such setup options then its design is obviously severely flawed and it ought to be redone (or find a better-written tool), I’m never going to be interested in having a tool that autoroutes motherboards not only because I don’t need to do those but primarily because I agree that is a poor use case for such a tool, but it certainly ought to be available for those simple projects which CAN benefit greatly from its capabilities.

Unfortunately I have done analog layout in the past but not either now or with this tool. Maybe you put a keepout zone around the area you’ve already done so it doesn’t get disturbed? I suppose you will also need to isolate or filter the power sources/ground for the analog part too, modern digital circuits aren’t as noisy as in the old LSTTL days but they can still “make quite a racket” if your other circuits are low-level, high-resolution or wide bandwidth. Other than that I’ll leave it for others with more recent and/or specific experience to comment.

I believe that you do any manual routing first, then export the DSN file. The DSN will include the routing you have already done. I guess you are referring to Manhattan style routing - i have limited experience of Freerouting but I believe that you set layer directions in the routing rules section
Any routing preferences are set in the autorouter itself NOT in pcbnew - the DSN file does not convey any routing preferences only the component positions and existing routing.

As I said, it is not simply a pushbutton solution but it does offer lots of options. Maybe your previous software was less flexible. However, with more options comes more choices to be made and more set up to be done. That may be a good trade off if you have a lot of a particular style of routing to be done.

Personally I no longer use an autorouter but believe that they can have a place.

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Thank you very much John & Jeff for your answers very comprehensive.
I have a good experience about analog pcb.And I know very well, it’s not enought a routing button to solve a pcb.
In the past I used Protel design system and, although of a very old released, it was a good cad.
Since few months I’m following kicad and I think to continue because it’s interesting.
You know Jeff I come from old school. Altought the new component have a good rejection to noise and analog problems, I prefer to continue with old advice or gnd and power division with different net from digital, isolated areas, filter, and so on.
In the next days I will try John’s suggestion with DSN solution that include my just done routing. It’s good for my application.
Thanks again John & Jeff.


The reason this is less parcticed now than in the past is that one is very likely to have signals crossing from one domain to the other. If one is not very careful about that one can easily create slot antennas. This is the reason why the current suggestion is to use an uninterrupted ground plane on an inner layer. (Separation can in some cases help but it requires much more work and knowledge than one might be willing to invest for questionable gain. This means the old “always separate” mentality simply no longer holds.)

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