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. 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 straighforward as theory? ;-) Erik (Who's only killed a few LEDs, but with little current, mostly.) -- I can only reply that I arrived at it by experimenting until I found something that works, and then stopping. - Rick Moen, on luv-main ------------------------------------------------------------------------------ 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
