555 EFI

[thergen at svn.net]

Picture an op-amp with the non-iverting input connected to pin 6 and the
inverting input connected to pin 5.  Pin 5 is also connected to a resistor
divider network that pulls it to 2/3 Vcc.  There is probably a symbolic
view on one of the semiconductor manufacturers sites.  I'm looking at the
cover of two different books that show this configuration. 

The 2/3 reference point can be yanked around to where you want by using
pin 5.  It can also affect the 1/3 reference for pin 2.

The pin numbers above assume the 8 pin package.

If you can't find an online reference, or it's still not clear, I could
probably try some ascii art to show the configuration.

Tom


On Sat, 16 Jan 1999, Clarence L.Snyder wrote:

> Bruce Plecan wrote:
> > 
> > -----Original Message-----
> > From: Clarence L.Snyder <clare.snyder.on.ca at ibm.net>
> > To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
> > Date: Friday, January 15, 1999 11:57 PM
> > Subject: Re: 555 EFI
> > 
> > >thergen at svn.net wrote:
> > >>
> > >> Bruce,
> > >>
> > >> Are you thinking of a string of one-shots and using a varying
> > >> voltage on
> > >> the control pins to vary the output pulse width?  If you're already going
> > >> to be using op-amps to scale the output of the sensors, you could
> > probably
> > >> add/subtract the outputs of multiple op-amps together through resistors
> > >> and run that into the control voltage pin of a smaller number of 555s.
> > >>
> > >question of clarification:
> > >what is the "control voltage" pin? My understanding of the 555 operation
> > >is the cap and resistance (cap between threshold {connected to discharge
> > >for monostable}and ground - resistor from B+ to threshold) were an RC
> > >"tank" circuit. The resistor controls the time required for the cap to
> > >reach 2/3 of B+ voltage.
> > 
> > Pin 5 sets B+ as you discribe it.
> > Bruce
> > 
> >
> What do I connect to pin 5, through what, to control this? On the info I
> have, this is the BYPASS pin and is tied to ground through a small cap
> to despike. How do I use it to control pulse width? What degree of
> adjustment is possible from this pin?
> 
> Another question -
> What percentage pulse width change would be required from the MAP or TPS
> input? What percentage from  engine temperature, assuming these were the
> only inputs you were going to use other than the trigger (tach sync)?
>