On Monday, February 20, 2012 11:39:08 PM Erik Christiansen did opine: > On 20.02.12 21:03, gene heskett wrote: > > Assuming its hooked backwards, how much normal one diode drop current > > going the wrong way does it take to kill a typical LED? > > Not much. Limiting the current to the microamps which I'd consider > (possibly) safe make it difficult to detect any output if it's the right > way round. So voltage limiting is much better. A resistive divider > across the 5v or 9v supply, giving e.g. 2.5v, and with a top leg > sufficiently low to give 10 mA in the LED, is a bit less destructive. > (Or, to reduce the resistor calculation part, a 2.7v zener (checked with > the voltmeter, to see what it's giving, once installed.) or 4 forward > biased silicon diodes to give around 2.4v on the low leg, provide a > safe testbed for opto stuff.) > > The 0.8V LED drop is fairly strong evidence that it was backwards, and > it's now a dead duck.
Nope, I had it right, but the wrong resistor, I had inadvertently let my hand come back out of the bag holding 150k R's and you have to be a Christian Scientist to think that would work. Kinda hard to bend my hand around to point at the guilty party, so I used a mirror. :) > Is this using the eagle macro I cobbled up for the HA2001? (I can't see > a way from the web page link at the bottom of your post, to the board > file. But I am GUI dyslexic.) I thought that we checked its polarity a > couple of times. > > Admittedly, the "boots first" approach should get the same result with > only one dead interrupter, since the second try has to be the right way > round. > > Why isn't practice ever nearly as straightforward as theory? ;-) That I believe, we can lay right in Murphy's lap. Which ought to be as hot as Micky D's coffee. Maybe that SOB would go pester somebody else for a while. > Erik > (Who's only killed a few LEDs, but with little current, mostly.) 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> Air pollution is really making us pay through the nose. ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
