2011 July 20

Almost ready to order

I got a reply from Custom PCB:

Yes, Eagle generates lines below 6 mils all the time. It is always up to the PCB manufacturer to fix it up to their minimum line width. So we don’t check against that because it is not something that designers can easily fix with their PCB software. But we do warn customer about silkscreen problems if their text is too small to be legible after increasing the line width to 6 mils minimum.

I just finished re-laying out the constricted ground wire. The narrowest constriction is 0.25″ now, but only for about 0.1″. The thermal calculator  can’t handle constrictions well—it wants to analyze under the assumption of an infinitely long wire 0.25″ long:

The trace width calculator uses empirical formulas based on long traces with no special heat sinking. … The trace width calculator is more geared towards long traces. Short traces with heat-sinking to planes do not get as hot.

It predicts a 30ºC temperature rise, but since I have a lot of heat sink nearby, I think that the temperature rise will be well under the usual 10ºC design guideline.

I also checked my vias with http://circuitcalculator.com/wordpress/2006/03/12/pcb-via-calculator/, which says that  27 mil holes with 1mil plating 62mils long should have a resistance of about half a milliohm and be able to carry about 3.4 Amps, so 5 such vias should be enough.  I have 11 or 12, which should be plenty.

Figuring out minimum trace width for a given voltage drop or power dissipation with http://circuitcalculator.com/wordpress/2006/04/20/find-pcb-trace-width-based-on-power/ might be useful in some other applications, but I’m less concerned about IR voltage drop than I am about temperature rise.

So, after I’ve gotten some sleep and had a chance to see if Gabriel or Steve can check my design, I think I’ll be ordering from CustomPCB.



  1. Kevin, it sounds like you’re back into the heavy (and incredibly messy) engineering details of implementing the KS algorithm! I don’t know much about the Arduino, but google searches show that others have successfully used it to implement “classic KS”, although very few people know about the “decoupled” version of the algorithm. Personally, I prefer “classic KS” because it’s more “elegant”, i.e. simpler. Remember that decoupled version was intended to overcome tuning problems with classic KS (while simultaneously giving independent control of decay rate), but both these problems can be solved within the framework of classic KS by the oversampling/decimation method we discussed over the phone a couple of years ago! –Alex

    Comment by Alex Strong — 2011 July 23 @ 06:41 | Reply

    • Alex, it is good to hear from you again!

      If you’d like to do a guest post on this blog, I’d be glad to have one, though the readership of the blog is still quite small—I wanted to get a few more posts up before I started announcing it on Arduino forums. I haven’t implemented either the original algorithm or the second algorithm on the Arduino yet—I got caught up in other projects (like the “hexmotor” H-bridge board for the robotics club). I decided to do a few things differently from how we did it on the old 8080, Z80, and TI9900 processors though, in that I’m making the sampling be interrupt driven rather than relying on timing loops. I’ve got as far as getting the DAC interface and simple wavetable playback working before I got sidetracked. I still have to write that up from my lab notebook as a blog post. Once I get that written up, I’ll start letting the Arduino community know about my blog.

      Comment by karplus — 2011 July 23 @ 10:07 | Reply

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