[Diy_efi] Ignition "ringing"

[Tomas Sokorai Sch.]

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

=2D-=20
Tomas J. Sokorai Sch.
Socio director, Gerente Proyectos Especiales
Xperts Ltda. F: 63 244591, Valdivia, Chile

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