efi555

dn dn at dlogtech.cuc.ab.ca
Sun Jan 28 23:16:08 GMT 1996


George M. Dailey wrote:

> I started having the same questions that are circulating around now about
> the 555.
> If I were still interested in building an EFI control unit from scratch.  I
> would seriously consider the Basic Stamp microcontroller by Parallax.  With
> 8 i/o's, you would have a lot more flexibility than the 555. Imagine:

I have some reservations about the Basic Stamp type processor. 
Firstly, with a BASIC interpreter running, you are burning up a
lot of processor time just running the interpreter, thus leaving
much less for your application.  I don't think the thing would be
fast enough to get microsecond timing resolution for the injector.

Secondly, you will need several analog inputs for things such as
temp, MAP, etc, and you would need an A/D converter for this. 
True, the Basic stamp has some Pseudo analog inputs in the form of
R/C timing on some of the pins, which would work for say, temp
inputs which are strictly resisitive, but not for MAP.

If I was going to design a processor based system, I would use an
68HC11, since it has all the nifty timers, A/D, etc necessary for
an electronic engine control (as a matter of fact, that's what the
thing was originally designed for...)  However, this would entail 
possibly hundreds of hours of writing code, testing, and
debugging.

The major advantage of the 555 type system is that it will run
just fine with no processor at all... thus your limp-home mode is
built right in to the system.  You can later add the processor
with advanced functions, and debug with impunity, and save a lot
of towing bills if it doesn't work first time around.  Also, you
can add, test, and debug one feature at a time, thus building the
sysem into an advanced engine management unit as time and money
permits.

The hardware approach doesn't bother me, since, as Steve Ciarcia
(Circuit Cellar Ink founder) says, "solder is my favorite
programming language".  I am, however, a reasonable HC11
programmer, but a complete fuel injection system is a major
undertaking.  GM spends billions on R+D for their systems,
with hundreds of programmers and engineers, along with all the
necessary toys to test it along the way.  I'm talking about
spending a few hundred on my daily driver and still being able to
drive it to work every day during the development cycle...

Regards
dn




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 Darrell A. Norquay              Internet: dn at dlogtech.cuc.ab.ca     
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