Datalogging RPM signal

[bcroe at juno.com]

If your coil has a ballast resistor to battery, you 
could get a pretty clean signal across it.  Of 
course its referenced to 12V.

Bruce Roe

> "Tomas" wrote:
>  
> > Hi, I'm writing an opensource program to plot HP
> > curves and monitor/log engine RPMs. I'm using a
> > voltage divider to pick the 12V signal from the
> > coil input. The input is recorded with my soundcard
> > using the Line input. I'm having troubles with
> > trying to figure out how to count the spikes,
> > because the signal I get is VERY far from a square
> > wave :). And with my ignition, when the RPM goes up,
> > the signal amplitude goes DOWN ....so no static
> > treshold for counting spikes :/.

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