> I seem to recall reading that knock sensors are far from
> trivial and that much signal processing and FFT's are
> required for effective implementation. If so, transplanting
> a knock sensor tuned for one engine onto a drastically
> different engine (inline six vs V6, solid lifter vs
> hydraulic, etc) is unlikely to be fully successful.
I've read much the same thing. Article I saw talked about the "knock
signature" being different for every engine. Apparently they don't do the
tuning in the sensor (which is basically just a microphone) but in the
attached computer/DSP. The more advanced ones also use a sliding window
algorithm that tracks the crank angles where knock is likely to occur, and
compares sound within the window to sound outside the window; in certain
frequency band(s).
Here's a chip that implements the simpler version :
http://focus.ti.com/lit/ds/symlink/tpic8101.pdf
Randall
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