On Monday, February 20, 2012 09:04:16 PM Ed Nisley did opine: > On Mon, 2012-02-20 at 17:42 -0500, gene heskett wrote: > > 4. All logic outputs with the slots open > > are sitting at about 18 millivolts. > > The doc says "a high output when the optical path is clear", so > something's definitely wrong... > > If that were my board, I'd expect the top-surface ground line running > barely 25 mils from the screw terminal pads to be at least mildly > shorted to all three output pins. Given the weak pullup, that'd hold all > three to ground. > > With the power disconnected, are all three outputs isolated from each > other *and* ground? With both polarities of the DMM? > To several megohms, yes.
> The bottom surface trace from the B terminal along those same pads may > give you a clue. Whip out a magnifier and check that clearance. > > If you have a duplicate unsoldered board, check that one out... Not yet, this is serial #1 :) > Is the board drawing (3 x 25 mA) for the LEDs + maybe (3 x 10 mA) for > the detectors? If the detectors aren't powered up, that's a hint. If > they *are* powered up, then their outputs are shorted to ground. They are powered ok. and any shorts under the screw heads aren't as there aren't any screws in it, yet. I have some phenolic washers for that. > The datasheet recommends a 100 nF cap "between VCC and ground near the > device". That probably doesn't make much difference in a test setup, but > I'd be superstitious and slap one cap in place across the board power > input. I considered that, in the form of pasting a 2.2 u-f tantalum in there, probably at the external interface connections. I have one laying on the assembly rug for that right now. > > Having just brought up a homebrew PCB, I never cease to be amazed at the > wide variety of things that can go wrong. Like having to scratch off a > tiny un-etched copper filament shorting a IC pin to ground *under* the > IC; it was visible, but just barely, only after I soldered the IC in > place. Before that, it wasn't there. [sigh] This one got etched a bit deeper, so there aren't any slivers, and there is a decent gap to help prevent solder bridges too. Thanks Ed. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> I'll eat ANYTHING that's BRIGHT BLUE!! ------------------------------------------------------------------------------ Keep Your Developer Skills Current with LearnDevNow! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-d2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
