Vats bypassed!!

[steve ravet]

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.


Pull high means that inside the ECM that pin is connected to +5 or +12
or some positive voltage through a fairly large resistor.  All you have
to do to drive that pin is pull it to ground.  Imagine you connected a
switch to that pin, with the other end of the switch connected to
ground, and you flipped the switch at the correct frequency.  When the
switch is off, you aren't pulling it to ground, which means the internal
"pull up" pulls it to +v.  When the switch is on you override the
resistor connected to +v and pull the pin to ground.  That switch is
called "open collector".  Open collector just means a circuit whose only
outputs are floating, or pulled to ground.  The transistor Pete talked
about will convert the 555 output into an open collector that will
properly drive the ECM pin.  If you get that part, like in a bubble
package from radio shack, you'll see three pins called base, collector,
emitter.  Hook it up like Peter said and you're good to go.


--steve

> 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
> > >
> > >

-- 
Steve Ravet
steve.ravet at arm.com
Advanced Risc Machines, Inc.
www.arm.com