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24929Re: [midatlanticretro] Re: What is "Runout"?

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  • Dave McGuire
    Mar 29, 2012
      On 03/25/2012 09:27 AM, josh6502 wrote:
      >> mistyped the DRC value as 5mil instead of 6...otherwise it would've
      >> caught it.
      > 6 mil traces??? I've seen electrons bigger than that!

      Most of my boards are laid out on 6x6 rules, 6mil trace width and
      6mil spacing. The processors I usually work with (in this case a
      Philips...erm, "NXP" LPC2387 ARM7 MCU) are typically in LQFP packages
      with 0.5mm spacing. That's about as tight as I like to go, but I do
      have a leadless chip (QFN package) with 0.4mm pad spacing that I'll need
      to solder soon. I'll get a good night's sleep before that has to go on
      the board.

      > Good going, and don't be hard on yourself, that's sometimes not such
      > an easy problem to figure out. Oh sure, we can all laugh about it
      > after the fact with the old saying "Did you turn it on?". I had a
      > similar problem, but with a twist, my circuit would work under some
      > conditions. Turned out, the chip was getting it's power through the
      > internal clamping diodes. When most of the inputs were low, the
      > circuit would stop... drove me nuts!

      Ugh!!! Circuits getting power through sneak paths SUCKS. At work
      recently we had a bus populated with bill validators and coin acceptors
      (an "MDB" bus), and the controller had to be able to power-cycle the bus
      when it hung due to EMI issues. (I know, treating the symptom...the
      real problem is being addressed now) The MDB bus was low-side switched
      (HORRIBLY BAD IDEA, but thankfully it pre-dated my arrival!) and the
      microcontrollers in the units on the MDB bus were never able to be fully
      reset because they were...you guessed it, getting power from the serial
      lines! Dammit.


      Dave McGuire, AK4HZ
      New Kensington, PA
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