Removing negative spikes selectively

[Thomashoej]

Hi,

So i am working on a rev limiter for my moped

In order to limit the revs, I need to remove the spark, which is done by shorting the negative signal from the pickup (a coil that essentially pulses at a specific point on every rotation). I've probed it and screenshot it, on my first attachment

My problem is, that I have no idea how I can remove the negative signal...
I though about using a transistor, but it turns out that it isn't too happy with -12v from collector to emitter.
i would've used a relay, but they are too slow. the signal will be repeating at every 4.5 ms.

does anyone have an idea to remove the negative signal, like on my second attachment (I manually connected a diode, to show what I wish for it to do)?

[Terry Bites]

A suitably rated diode with a series resistor should do it. You could add a comparator- this will ignore the negative part of the waveform completely.
eg