Help Please!!!

[Jim Staff]

  Hello. I'm working on a system for super mileage vehicle competition, and I 
need to build an injection system. And I was wondering if I could get help from
 
the people here at DIY_EFI. I'm an electronics guy and have no clue how this 
automotive specifics stuff works. So I'll give you a rundown on what I have to 
work with and if anyone could help me you could reply to DIY_EFI server or to m
e
personally at Staffj at freenet.msp.mn.us.
  
  Basics
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Engine : Briggs & stratton 3HP, 4 cycle single cylinder (Wow huh?)
Intake : Carb.
Ingition : Briggs & Stratton's Factory Points Ignition.

Notes : Exactly the same engine you'll find in 90% of the lawn mowers in the 
world. It runs like a pig and is a massive gas hog. The compression ration as 
measures was Å8:1 and I know it runs really rich.

Modification : I have a second PTO shaft that is infact the cam shaft. It 
provides a single RPM/Power cycle. That way I don't have to arbitrate the 
exhaust and power strokes.

 Advanced
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Modification 1--Tachometer.
    The Tachometer I'm going to use is as good as finished. I thought it was 
best to use a Hall Effect sensor as a pickup on the cam shaft. This is then put
 
through a devide by 10 and a devide by 5 then it is inverted and fed as an 
interupt into my computer system.

Modification 2--Electronic Ignition.(Or at least better ignition)
    Since I have to have a car battery on theis thing anyway, I want to replace
 
the Briggs standard points ignition system. I'll replace it with a pickup coil 
system and a switching modual from an GM car and a ignition coil from a Ford. I
 
think I'm trigger it with a hall sensor on the cam shaft just before the piston
 
reaches TDC, I'll make the sensor movable so that you can adjust the spark 
advancement by hand. I thought alternatively I could have that sensor act as a 
sentinal and make the computer time it. But since I'm using a 286 PC I can only
 
get hundreths of a second from the RTC. I was wondering if this is an OK amount
 
of slack? Well anyway anything is a good replacement for the points system.

Modification 3--EFI
   This is were I get completly lost. I know that injectors take Å+5V at a good
 
chunk of amps. They run on a square wave duty cycle. I don't know how I could 
create this duty wave from my digital output. Since a bus cycle is a specific 
amount of time I can't hold the bus. And I have no clue how a real ECU does it.
 
I could use a lot of help here. If there is any specific or general stuff you 
know I'd like to hear it. I do believe that on the market somewhere there has t
o
be an IC that turns an 8 bit binary number into a pulse width for the injector.

Modification 4--Feedback for the EFI
   I need help in this area too. I know that an O2 sensor provides a voltage 
based on the amount of air present in the exhaust. I'm going to sample this wit
h
an analog to digital converter. Most of them are +1.2 V to +.1 V so my sources 
tell me. I haven't pinned down a MAF sensor yet but I believe that they are als
o
voltage analog signals, so I can do the same thing with this. If it's not could
 
you please tell me what it really is and how to change it into some kind of 
voltage. The last thing I want to have is a temp sensor that way I can calculat
e
the true mass of the air going into the engine. Then I can solve the equation 
for x (amount of gas needed) and inject it.

Mod 5--LCD display
   I want to use a standard 16x2 LCD line display and have it track RPM and MPG