Vats bypassed!!

[Jim Fitzgerald]

Mike,
In general an "open collector" circuit refers to an input that is already at
some non zero voltage with nothing connected to it.  It is usually "pulled
high" by an internal "pull up resistor" to a voltage source.  The actuating
signal must "sink"  or drain current out  to provide a signal.  A regular input
would have a terminating resistor to gnd, and be at 0v. The actuating signal
must then "source" a current.  The resistor in both cases determines the input
impedance, and how much current is needed, and what driver should be used.  TTL
circuits come both ways, just match the current sink or source capability.  The
transistor driver circuits can also be configured either way.

Mike Rolica wrote:

> What???  I really appreciate you help  but you have got me lost.  Is this a
> transistor you are talking about( 2N3904)? If so is it a npn or a pnp? what
> do you mean the "input is a pull high" and what is "drive with a open
> collector" what does this do??? Sorry for my ignorance.
> Btw  this timer sometimes works but takes allot of cranking,  is I
> disconnect and connect the +v to the timer repeatedly while cranking it
> starts better or I should say sooner.  Why would this be?
>
> > -----Original Message-----
> > From: thergen at svn.net [SMTP:thergen at svn.net]
> > Sent: Thursday, September 09, 1999 8:35 PM
> > To:   gmecm at efi332.eng.ohio-state.edu
> > Subject:      Re: Vats bypassed!!
> >
> > Pin 7 of the 8 pin 555 is open collector, I think.
> >
> > Tom
> >
> > On Thu, 9 Sep 1999, Peter Fenske wrote:
> >
> > >
> > >
> > > Hi Mike
> > >
> > > What you need is as near a 50% duty cycle as you can get..
> > >
> > > The drive to the vats input is also a pull high..
> > >
> > > This means you must drive with a open collector..
> > >
> > > Translation.. use a 2N3904, drive the base with a 1K to your 555 output.
> > > ground the emitter and tie the collector to the vats input.
> > >
> > > This should make your girlfriend much happier
> > >
> > > :peter
> > >
> > >
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