[Diy_efi] Re: Ignition "ringing"

MiseryQ MiseryQ at miseryhq.d2g.com
Sat Apr 26 00:35:35 GMT 2003


I've had a problem getting a clean signal... I used a separate GM HEI
module to trigger the controller... On the scope it gives an almost
perfect square signal...

Q..

The "ringing" you're talking about is the energy sent to the primary
stage = of=20 the coil when the magnetic field of the coil collapses
after removing the=20 power. This collapsing magnetic field is what
makes the coil work. The main= =20 idea is that the collapsing magnetic
field induces the high tension on the= =20 secondaries of the coil, but
as the primaries and secondaries are wound ove= r=20 the same inductor
core, it also generates a nice voltage spike on the=20 primaries. A good
method to filter this spikes ( It's not a single spike, i= t=20 has a
high frequency) is to first clamp the voltage and then pass the signa=
l=20 thru a RC filter to cut frequencies above certain threshold (maybe
someone= =20 with more EE background should correct me on this). Take a
look at the desi= gn=20 used to pick the signal from the coil for the
tach input used in the=20 Megasquirt project. But-=AD--- the signal
conditioning of these signal is=20 pretty tricky. I've tried many
different approaches for getting a nice squa= re=20 0-5V signal, but I
got a very limited the success :(. I tried Dennis=20 Noordsij's (from
this list) recommended circuit=20
(http://www.bubblesoftonline.com/projects/points.html), the one from
the=20 Megasquirt input (http://www.bgsoflex.com/megasquirt.html) and
some=20 variations over the idea of using the ne555 in monostable mode
(like the ta= ch=20 circuit in
http://members.shaw.ca/tsmit/tachmod/tachmod.html).
The circuit that worked over the broader RPM range was the Megasquirt's,
bu= t=20 still was absolutely unusable for triggering my uC input to log
RPM reliabl= ey=20
(sp.?) over my engine's RPM range. You might be more successful as you
use= =20 other ignition (mine's a '75 Ford Duraspark I).=20


Sincerely,

Tomas


On Thursday 24 April 2003 18:52, Chris Ice wrote:
> Hey all...I'm trying to capture a clean ignition signal and have had 
> trouble doing so.  Have had in two cases...digital recording for 
> feeding homedyno (thru either induction clamp or voltage divider 
> across the
> coil) and another as an rpm signal to my maf signal conditioner from
> coil negative.  In both cases the signal is very noisy, and I'm told I
> have "ringing" going on in the ignition.  The car runs fine tho, as
does
> my dash tacho (very "old world" 1977 tach).
>
> This is an '80s GM HEI style electronic ignition, so has the somewhat 
> boomerang shaped ignitor module with a standard looking ignition coil 
> and what appears to be a noise cap attached but doesn't appear to
work.
>   Is on a Fiat/Lancia product in case you care. ;)
>
> Any background information or suggestions afa. elminiating noise in 
> the ignition circuit so I can get a clean signal?  Or just general 
> information on where noise comes from?
>
> Thanks!
> Chris




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