strange 556 behavior - trying to flash LEDs

mrdarrett · 2008-06-06T18:03:52+00:00

Given two LEDs, I wanted to build a circuit that would alternate inturning those LEDs on and off, with only one LED on at any giventime. LED 1 on, LED 2 off; LED 1 off, LED 2 on.I have a few 555s and one 556, so I thought to use an astablemultivibrator.I saw and built this circuit:but was a little bit irked that a small amount of current still leakedthrough the first LED to activate the second transistor, and I couldtell the first LED didn't quite turn off all the way.So I built my own circuit, using the second part of a 556 as a NOTgate:It worked just fine for about a day or two, but then I noticed that Q2stayed on ALL the time, while Q1 blinked on and off.At first I discovered a loose ground, and thought that was it, butthen the problem repeated.Then I thought my 2N3904 transistor blew out, so I replaced it - butstill the same situation.Did I blow out my NOT gate somehow? I don't have another 556, so Ican't test that theory yet, but that's where my suspicion lies.I'm using 4 1.5V AA batteries as the power supply.Any ideas?Thanks,Michael--Consider: A million and a half new Americans are murdered every yearby abortion. No other issue involves numbers that high. Nothing shortof a full-scale nuclear or biological war between well-armed nationstates would kill that many people, and we aren=92t in imminent dangerof having one of those. Jobs? The economy? Taxes? Education? Theenvironment? Immigration? Forget it. We do not have nine millionpeople dying in a typical president=92s term of office due to bad jobprograms, bad economic policies, bad taxes, bad education, badenvironmental law, bad immigration rules=97or even all of thesecombined. All of them together cannot provide a reason proportionateto the need to end abortion. Make no mistake: Abortion is thepreeminent moral issue of our time. It is the black hole that out-masses every other issue. Presenting any other issues as if they wereproportionate to it is nothing but smoke and mirrors.

Jun 06, 2008 22 Replies

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John Fields 18 years ago

Yeah, yeah, I know... Sometimes I get stupid. Thank goodness you and Speff are out there to catch the errors and point them out without rancor. :-) JF

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Jim Thompson 18 years ago

It was actually the first thing I thought of, then OOOOPS !-)

...Jim Thompson

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ehsjr 18 years ago

D-uh. Maybe I should open my eyes when I read the threads. :-(

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