switching circuit for crank ref. signal needed (please help)

[auditude at neta.com]

Hello people,

My name is Ken.  I just joined this list a couple of weeks ago.  I 
still have to delve into the archives and try to get at least a little bit 
up to speed on what's going on.  But I already have a question, and 
a request for help if it's available.  I hope this is an appropriate 
forum for these questions, and that I'm not violating any list policies 
that I should have paid more attention to when I joined.

I've got a project started which involves converting an '88 Audi 
5000CS turbo quattro motor over to standalone EFI.  This is a 5 
cylinder turbo motor that originally comes with Bosch CIS to 
handle fueling.

The standalone EFI is the LinkPlus by http://www.link-
electro.co.nz.  This will be my first project of this type, but I'm 
optimistic that at least the installation will not be too bad.  The 
tuning may be another story, but one step at a time.

Anyways, just about all of the configuration questions that I'm 
aware of have been addressed, except for the cam sync signal that 
tells the ECU when cylinder #1 is at TDC on the compression 
stroke.  It would be easy enough to take the sync signal from the 
hall sensor at the distributor, but I have a better way in mind that 
mimics the way the stock ignition system work on the car.  

Basically the stock ignition uses three sensors (by the way, much 
of this information is MUCH thanks to Orin Eman, who is/was on 
this list and has been helpful to me so far).  

1)  There is a magnetic reluctance sensor for RPM that reads the 
flywheel teeth as they go by, all 135 of them.  

2)  There is another magnetic reluctance sensor that sends a 
signal when a pin on the flywheel is at 62 degrees BTDC for 
cylinder number 1.  And,

3)  There is a cam driven hall sensor that sends a signal that is 
about 40 degrees in duration, centered on the 62 degrees BTDC of 
cylinder number 1, "but only on the compression stroke".  This is 
used in combination with sensor "2" above to give precise 
information about crank position and cycle.

The stock system uses these three sensors to figure out rpm and 
crank position, so that it can fire the ignition at the right times.

My needs will be for even more precision, pretty much, because I 
will also be running full sequential fuel injection (stock CIS is 
"constant"), and later on direct ignition using 5 coils.

So, the ECU manufacturer, Link, wants me to use "only" the cam 
hall sensor for the sync information.  I say that's an unnecessary 
step backwards from the stock system, as far as accuracy of 
crank position.  This is due to the timing belt and gear drive adding 
potential slop and altering where the hall sensor signal is in relation 
to the crank.  

Not to mention that with the stock setup, the distributor only has to 
be "close" in order for the engine to fire and run.  With it being only 
"close", the ignition timing is still perfectly indexed with crank 
position, since the cam signal only tell the ECU whether the next 
crank signal is compression or not.  "Their way", if I loosen my 
distributor and rotate it anything from what I tell them it is at when 
they configure the ECU, the whole system will be off by a 
considerable amount.  Not cool, IMO.

So, I figure all I need is a simple circuit, where the cam hall sensor 
signal controls whether or not the signal path from the crank 
position sensor is connected to the ECU.  If the distributor is not 
facing the right direction, the circuit is open and the crank signal 
doesn't get to the ECU (exhaust stroke).  If the distributor is facing 
the right direction, the signal path is complete and the ECU gets 
the signal telling it that cylinder #1 is (approaching) TDC on the 
compression stroke.

I would use a big ole relay if I thought it was fast enough and robust 
enough for the application.  I am not an expert on electronics, but 
I'm sure some sort of circuit could be put together that would 
accomplish what I want.  The response time would only have to be 
as fast as cam speed, and it would have to be controlled by the 
hall signal, and only be beefy enough to carry the little 5v output of 
the magnetic reluctance sensor picking up the presence of the 
flywheel pin.

I suppose worst case (or second to worst case since I could just 
use the hall signal), is that I could go to Radio Shack or something 
and ask the people behind the counter for their guidance.  However, 
I'd rather hear what you folks had to say on the matter, since  what 
I've read here so far indicates this is very simple stuff compared to 
what you can solve.

It seems simple enough for me to try to set it up this way.  It's only 
slightly more work than just using the cam hall sensor alone, but 
I've never made little circuits like this.

I'm eager to hear any thoughts or advice on this.  Maybe there's a 
product out there already that does what I'm looking for.

Thanks!

Ken Keith

----- End of forwarded message from owner-diy_efi at diy-efi.org -----
----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org