[Diy_efi] 555 Timer controlled EFI

[Geoff Harrison]

Good comments Daniel. I did see your other post regarding the 
size of MAFs. And it stands to reason.
When I first looked into this idea, I was looking for a 
replacement for a typical 2 barrel carb on a typical 4 litre 6 
cyl. The more I learnt about GM controllers, the more I felt I 
was re-inventing the wheel. If I were to use GM sensors 
everywhere, why not just use the controller and harness, and 
learn how to program it.
So it got shelved. It still has the advantage of being easily 
tuned, especially if a WB02 is used.

As for the learning curve, I think I learnt more about EFI in 
starting to design one, rather than just using one from the junk 
yard, with the aid of these posts. Several listers have ideas 
about using the idea on single cyl or stationary engines, it may 
shine in that area.

As I have stated earlier, this is just an idea I have not yet 
prototyped. What I can say though, the 555 can be a bit tricky 
when mounted on Vero board. You must run bypass caps on the 
supply rail. When it resets, or discharges the timing capacitor, 
it can cause a surge, making the pulse length inaccurate. I have 
heard of the 555 being a bit unstable. Could be the same cause.

Geoff H.

PS please don't ask me to define a typical 4l 6cyl eng. LOL. Try 
a 70s. Silly comment this day and age.

----- Original Message ----- 
From: "Daniel R. Nicoson" <A6intruder at myo-p.com>
To: <diy_efi at diy-efi.org>
Sent: Saturday, January 21, 2006 2:50 PM
Subject: RE: [Diy_efi] 555 Timer controlled EFI


>I haven't been following your discussion throughout but I'd 
>like to offer a
> couple comments.
> First I think it's an interesting idea to base a EFI around a 
> 555 but I
> don't think it is very practical.  With the price of the 
> lowliest 8-bit
> micro processors less than $5, you're going to make yourself 
> crazy making it
> work compared to going with a simple digital system.  To much 
> stuff is not
> linear...
>
> Enough negative.  Here's a couple positives.
>
> 1) If you are going to run an engine with a 555 chip, the 
> "restriction" of a
> MAF is the least of your problems.
>
> 2) If you size a MAF for the engine at hand, it is not a 
> restriction.  By
> sizing it, you have ensured it will flow more air than your 
> engine can
> possibly use.
>
> 3) If you want a MAF with an analog output, use a Ford MAF. 
> The use 12 volt
> power, a 5 volt reference voltage, and they output a 0 - 5 
> volt signal.  No
> it is not a linear transfer function.
>
> 4)  Has anyone started bread-boarding this controller?  It is 
> interesting
> what you learn as you are bread-boarding circuits like this.
>
> Good luck,
>
> Dan Nicoson
>
>