jremington:
Since the spark plug signal is tens of thousands of volts
I may have not been clear. I am not using the spark plug signal itself. I am wrapping a wire around the cable that goes to the spark plug, so that a pulse is induced in this wire each time the engine sparks.
jremington:
The posted scope image tells me nothing, but I wonder what the nasty spikes on the blue trace mean.
The nasty spikes is the induced pulse that occurs each time the engine sparks. I posted the scope to show the clean signal circuit does output a square wave with the same frequency as the spark plug signal.
jremington:
Everything but the electrically shielded sensor wire should be in a grounded, conductive enclosure.
All the electrical connections are on the Arduino shield which sits on top of the Uno. I didn't think noise would be an issue.
I've posted another schematic showing how the circuit is powered and connected to Arduino. If I've left anything important off please let me know what else you need. Thanks for your help!
