555 EFI again...

[Walter Petermann]

Webb Family wrote:
> 
> Sorry to but in here, but an off the wall idea just occurred to me.
> 
> You were talking earlier about how hard an analog multiplier is to come up
> with. At the same time, you are worried about this "unwanted" logarithmic
> charge characteristic.
> 
> If you set up the 555 so that the time between sparks is the cap charge time,
> cap discharge time is the on time for the injector, and the tps controls the
> CAP charge voltage, is that not the analog electronic equiv. of the
> mathematical operation of adding the logarithms of 2 numbers to multiply?
> 
> I hav not thought this through - it was just an off the wall idea, but...
> sometimes a 555 can be the basis for a really elegant simple circuit. Is this
> one of those times??
> 
It sounds very worth looking into. I have spent a few minutes TRYING to
put down what you are saying into 555 timing equations. I do get the on 
time as a function of ln(trigger voltage)-ln(MAP) plus some extra 
terms. Will come back after breakfast and redo the math...need a + 
sign in there. However, if it does turn out to be the sum of 2 log
numbers, it looks like you'd still need to generate the inverse  log
to get the final answer.
oops! This doesn't pass my count to twenty before pressing "send" test.
What's needed is ln(RPM)+ln(MAP). My rpm is in those "extra" terms.
Oh well, off to breakfast.

Walter