Author Topic: KiCad 5.99 trace length tuning  (Read 869 times)

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Offline Mario87

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KiCad 5.99 trace length tuning
« on: October 14, 2021, 06:54:15 pm »
Hi all,

Already asked on the KiCad forums but got no response, so hoping someone here can help. I am Pretty new to KiCad, but have used other EDA tools previously. First time I am using KiCad to tune trace length. Had it set to tune each track to 12mm and it appeared to work fine, but the strange thing is if I click on the “tuned” traces with the tool after I set the length required, it then tells me the trace is longer or shorter than specified.

Example in the attached image, this trace was set to 12mm give or take a about 0.05mm but now it is “Too Long” and 0.8mm out of spec.

What is going on here? Is it me, or just a bug in 5.99? Full version I am using is: (5.99.0-11663-g8172737d6f), release build.

Thanks

 

Offline Kleinstein

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Re: KiCad 5.99 trace length tuning
« Reply #1 on: October 14, 2021, 07:42:55 pm »
With the rather fine wiggles in a relatively thick trace it is not that obvious on how to define the actual lenght. There may be different methods used to calculate the length and 1 or both may be wrong.
 

Offline Mario87

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Re: KiCad 5.99 trace length tuning
« Reply #2 on: October 15, 2021, 09:14:39 am »
True, but I do suspect there is a bit of a bug in KiCad and the reason I say that is sometimes when I had the straight traces (before tuning the length) it would show as being 16mm long, but if I deleted the trace then made an identical new one it would magically become 10.2mm long and I could then do proper tuning of the trace length.

Think I will just use it as-is and hope for the best, it's just an expansion board for my FPGA dev board, so not an issue to re-spin if I need to, but I do hope KiCad fix this issue. Might actually download the latest nightly build and see if it's any better as this one is a couple of months old now I believe.
 

Offline golden_labels

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Re: KiCad 5.99 trace length tuning
« Reply #3 on: October 16, 2021, 11:06:42 am »
I am still on the stable release (5.1.10), but if they work the same: KiCad is producing the pattern according to constraints set in track’s properties. Those constraints limit the solutions space. Some lengths may be impossible to achieve with the given restrictions.

You may adjust various parameters on the fly while drawing wiggles by pressing keys 1 to 4.

I concur that with tracks that thick and wiggles that tiny the length is hard to define. Unless this is an RF circuit, of which I do not know enough to comment, some portions of those tracks are acting more like variations in track width than length increase.
« Last Edit: October 16, 2021, 11:20:21 am by golden_labels »
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