Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!aramis.rutgers.edu!topaz.rutgers.edu!hobbit
From: hobbit@topaz.rutgers.edu (*Hobbit*)
Newsgroups: sci.electronics
Subject: Vaguely related to the light bulb problem
Message-ID: <Jul.20.00.01.34.1989.25586@topaz.rutgers.edu>
Date: 20 Jul 89 04:01:35 GMT
References: <4363@merlin.usc.edu> <1348@bnlux0.bnl.gov>
Organization: LCS Expert gang, Rutgers
Lines: 20

What's the correct way to drive TTL from an op-amp?  I'm proposing to do some
kind of threshold detection by sending an op-amp output into a Schmitt; the
op-amp seems unable to pull *low* enough to make the Schmitt input see
a low level.  I suppose I could go out and buy one of those fancy op-amps
that drives all the way to the - rail, but I'd rather have a simple fix I
can do from my junkbox.

The only thing that's worked so far is something like

	        .1 uf
	|\   +---||---+
  opamp	| >--*        *-----> to schmitt input
	|/   +-v^v^v^-+
	        1k or so

... which apparently creates a pulse low enough to kick the schmitt down if
the falling edge is fast enough, but s'pose I want to respond to an output
that drops more slowly??

_H*