Has anyone used a PIC to sense RPM using the contact points (a.k.a. p-lead) on a mageto? I have built and coded a tach but now have an issue sensing the transition (Yeah, I know I should have looked into this first ...). I have tried a zero-crossing detector, level comparators and a few filters. Still can't get reliable triggering.
I get about 200V positive and negative pulses on the line. Fed the input through diodes, a resistor network and a zener for clamping, but the LC oscillation as part of the process is making it really difficult to sense the spark point (point where the points open).
I'd appreciate any suggestions ... thanks,
Shane
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