TattleTales

Lino Verna lino at sequoiasci.com
Wed Mar 18 17:58:54 GMT 1998



>Lino Verna wrote:
>
>> Also if anyone would like to give me a hand with the spark issue I would
be
>> in your debt.
>
>Lino, whats the problem?????

I guess I should have made the issue a little more clear before asking for
help...
People are always telling me to ask them the question before demanding the
answer....   Maybe I am ready for that hat...

Anyway here is the situation.  This tattletale has a neat little function on
one of its i/o lines that will count waves of a cyclic input or tell you the
frequency of the input.  Anything up to 30KHz.    Plenty fast for even a 120
tooth sprocket on the crank at 10000 rpm.
So I can get RPM with no trouble.  If I am not going to use timed sequential
injectors, I dont need crankshaft pos.  So I don't need any other high speed
digital inputs.  The rest are analog signals from TPS or MAF depending on
how you go.
Am I doing OK so far?  Please correct me if I am wrong.

Spark control is a little more picky.  It pretty much requires knowing where
the crank is to within a degree or less  (Is that right?).    So I assuming
that I (at this point) dont really want to add any additional processors  I
need to figure out how to get the tattle tale to know where the crank is.
If I have it count the teeth on the crank wheel and leave a gap at some
point, then it'll know that after it sees so many peeks,  (it can stop
counting at a given number) that it has reached the gap in the wheel,  then
it knows position, then if it divides the degrees on the crank that have
teeth by the time it took to count it'll have RPM.  Then it can start a
timer to fire an injector after a certain amount of time ( based on rpm and
load and...)
Now the problem I see here is that all these things have to happen in a
pretty little amount of time.  I really have no idea whether the tattle tale
can work that fast  and still keep track of injection duties.

Maybe having a dedicated PIC working realtime and letting the tattle tale
provide timing numbers or injector durations is the solution.  As Robert
Harris suggested in a recent post.

I have a hunch that answering this question may require a little more
familiarity with this here tattletale thing than you all may have OR WANT.
That I can understand perfectly.  If it is possible to give me a hand
though, I would appreciate it.

I'll be busy for a bit changing gears here because I see a pretty steep hill
coming at me in the learning curve.



Thanks again

lino




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