555 EFI

[Clarence L.Snyder]

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. A variable voltage will not do this properly.

If the control voltage on the threshold pin drops below 2/3 supply
voltage, you do not get a trigger.

How about running the 555 with a "floating ground" from 12 volts, and
the "threshold" or control voltage anchored from ground? As long as the
control voltage cannot exceed the supply voltage  it should work. By
varying the "floating ground" with a variable negative voltage regulator
you would have one input, and varying the threshold voltage source
(through a resistor) using something like a MAP sensor or TPS you would
have a second input. Varying the charge current control resistor would
give a third input.

Vary the source voltage, or "floating ground point" according to
temperature, charge voltage according to MAP or TPS, and charge current
resistor for "mixture control" fine tuning ( thinking of aircraft apps
here) and it might be doable? Mabee use an O2 sensor to feedback control
this fine adjustment for automotive use?

Let's hear the feedback.