At 11:16 AM 6/12/01 -0400, you wrote:

>I am tinkering with an ignition system for a car, and want to include a
>knock sensor.  I imagine that the knock sensor is putting out some sort of
>signal all the time, and you have to isolate the knock from other engine
>noise, etc.  Does anyone know what an "knock" or "ping" looks like, and
>the type of circuit that might be used to [robustly] detect it?

I don't think you'll have signal analysis problems, modern knock sensors
are just piezo "microphones" that pick up the rather severe mechanical
"detonation" in the kHz range. Expect output signal in the 1-volt range,
give or take. You can simulate knocking by tapping the engine block with
a hammer.

You can model it as a ~1nF capacitor in series with a voltage source to
the terminals, with a few megohms in parallel.

You'll need shielded cable to it, of course.

Best regards,

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