simple analog fuel injection comments from CSH, HQ

[goflo at pacbell.net]

Bruce Plecan wrote:
>  I wish someone would start a thread on what the hell to do with
>  a PIC. 

>> For an intro to the subject you might take a look
>> at the BASIC STAMP 1, made by Parallax. 
>> A PIC-based microcomputer programmable in a flavor of BASIC. I'll bet 
>> a sparkling beverage-of-choice that a Stamp-based EFI that'll run is 
>> do-able.
 
> Again, would be nice to get a distilled version.  Also if you have some
> insight to how to execute this it would be great to hear.

I like the distilled stuff too, but try not to...
For distilled Stamp stuff there is a ton of info on Parallax' site, and
the Stamp list. Strong suite of device is simplicity and ease of use,
though.
A little hands-on will obviate a lot of palaver. Recommend Version D,
which can be snapped onto a 9 volt battery, and has a little prototype
area.

Per insight into Stamp EFI: Let's assume one cylinder for openers. For a
speed-density lash-up we need to know rpm so let's drill a hole in the 
flywheel and press in a small cylindrical magnet. We'll mount a pick-up
coil on the crankcase adjacent, clean up the coil output with a schmitt 
trigger, and feed it to a stamp i/o pin. When the stamp needs to know
rpm 
it executes the PULSIN instruction, which waits for the rising edge and
then counts off 10 usec increments till the falling edge. PULSIN value
is
inversely proportional to rpm. MAP could be acquired in a similar
fashion,
by using the output of the MAP sensor, with suitable filtering, to drive
a voltage-controlled oscillator and then measuring the pulse width with
the
PULSIN instruction. Temperature can be read with a thermistor RC network
and The POT instruction.
At this point we know what we need to know to calculate injector-on time
with the speed-density algorithm. Foo factor is arranging terms so as
not
to exceed the 16-bit math of the stamp. Forgive me if I don't attempt it
this moment - Way past bed-time.

I don't suggest for a moment that the stamp is a suitable platform for
such 
an application. Simply that the minimal programming overhead of the
device 
allows one to concentrate on solving the problem at hand. 

Jack

BTW, did I mention all the Parallax stock I own? I wish :)