Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucsd!brian
From: brian@ucsd.Edu (Brian Kantor)
Newsgroups: sci.electronics
Subject: Re: 555 IC Timer help needed
Message-ID: <10046@ucsd.Edu>
Date: 7 Oct 89 19:21:28 GMT
References: <169@uwm.edu> <568@limbic.UUCP> <3356@ccnysci.UUCP> <29060@buckaroo.mips.COM>
Reply-To: brian@ucsd.edu (Brian Kantor)
Organization: The Avant-Garde of the Now, Ltd.
Lines: 13

Things to keep in mind when dealing with 555s in any kind of precision
application (besides deciding to use another part, heh heh heh) is that
you are working with a chip that has lots of high-gain op amps in it
right alongside a really beefy digital output structure.  Bypass the
hell out of it.  Don't leave pin 5 unconnected; bypass it.  And it
doesn't hurt to put a bit of isolation on inputs from the real
world; I'd use opto-couplers, LS14s, or sink resistors and diodes 
(in order of decreasing effectiveness).  The lower the impedance of the
input the less likely it'll false trigger.

If you can transmit with a 5-watt CB next to the unshielded 555 circuit
you've designed without ill effect, you can feel proud.
	- Brian