Old 486 Board for ECU??

[Axel Rietschin]

----- Original Message -----
From: "Gavin" <gavston at sprockets.freeserve.co.uk>
To: <diy_efi at diy-efi.org>
Sent: Tuesday, May 30, 2000 9:59 AM
Subject: Re: Old 486 Board for ECU??


>
> >ECUs are all about timing. Something PCs, no matter how fast, are not
> really
> >good at.
> >
>
> Is this the actual PC hardware, or is it the OS that would run it the
thing
> that wouldn't be very good?

Probably a bit of both. Of course, it depends of what you want to do but I
can imagine a few headaches just to find out and maintain the exact crank
position at all times, including while the engine speed is changing fast.
Also, you need a lot of time-related functions to drive your injectors,
ignition coils, EGR valve, boost control valve, air bypass valve, variable
cam, you name it. Precise pulses and PWM signals are difficult to generate
in software, unless you tolerate random amounts of jitter and a few misses.
On the OS side, I don't know which PC-based system would do. You probably
better off writing the control software right on top of the BIOS.

If the hardware could tell where the crank is, read frequency-based sensors
(air flow meter?), compute wheels speed, generate PWM signals and handle
output pulses in such a way that you just say when in crank degrees and for
how long in microseconds, this would free up a lot of CPU cycles for you to
code the funny part, like closed loop fuelling and boost control, start
line, limited slip, anti-turbo-lag, gear change and detonation strategies,
data logging, dashboard communication, to name a few.

For a basic batch-fire injection system, with not-so-tight spark timing and
few control functions, if any, a PC with an A/D board and suitable output
drivers hooked up to the parallel port could probably do, up to a certain
extent (someone mentioned idle, which is already great!) . If it doesn't
work as intended, you can always recycle it to control home appliances :)

That said, there is no doubts a PC can boot without a hard disk. You can
write your own BIOS with POST and bootstrap routines that suit your needs.
Also, there is plenty of space in a typical car to fit even the largest PC
motherboard and you can always use a standard PC power supply with a
12V-to-110/220 converter in front of it. Last, a 3.5" floppy is certainly
big enough to hold the largest engine control program and huge maps, except
maybe if you are coding in Java(tm)

;-)

--Axel



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