555 EFI

[Bruce Plecan]

-----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

 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.
>