[Diy_efi] PC-laptop based efi

[peterw]

> Hi, i'm looking into the possibility of designing a efi control system
that
> would run on a laptop. I think that it would be of the multi-port variety.
In
> order to avoid windows-timing issues, i have been thinking of using
dedicated
> microcontrollers to actually turn on and off the injector. Basically the
PC
> would take in sensor inputs, and compute the required pulse width for the
> injectors, and send this to the microcontrollers, which would turn on the
> injector for the required duration at the correct time. Does anyone know
any
> basic flaws in this design? I like it because it could provide a real-time
> user interface with the efi controller, so tunning, and diagnosing should
be
> easier. Also, i think a laptop running the engine would just be cool! Any
> input would be greatly appreciated.
>
> -Matt
>

Speed and timing may bring you undone. In order to read sensors, lookup
tables, do calculations you will need a fast machine running a true real
time operating system, especially if you are doing lookups and calcs every
rev or every second rev. At 10,000RPM a rev takes about 6 milliseconds. This
may fine on a fast machine untill the OS wants to flush the disk cache or do
some other such system thing. Note Windows and Linux are not real time
operating systems. Not only does Windows not know about hard, preemptive
scheduling it randomly decides not to work( I think this may be based on the
phases of the moon). Linux can be made hard real time with kernal patches
and an API lib.

You may get away with it if you use MS-DOS(no multi-tasking) and treat the
laptop as a big microcontroller. But if you do that you might as well just
use a micro like in the Megasquirt et al.

I am currently experimenting with a small(Compaq Aero) laptop running Linux
to do some engine data logging from microcontroller sensors. This works fine
'cause the micros buffer the data and the laptop just acts as a big storage
device. No time critical calcs are being done and nothing is being
controlled.

Peter.


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