Knock alarm

[Chris Conlon]

Tony Cooper wrote:
>
> David Piper wrote:
> 
> > Can someone comment on the availability of a knock sensor alarm.  Which
> > sensor would have universal applicability?  How could I fab a circuit to
> > ...
> 
> You may have a problem here. 
> The sensor sounds about right, but you will have a problem making a
> generic system. 
> All engines knock at different frequencies - no 2 engines are the same.
> What you need is
> some intellegence built into the system, something like a DSP would do
> the trick, but even then
> the system may need some 'tweaking' just to get the correct frequency,
> and that would only
> ever work on that engine. Even aging can move the frequency of knock.

Is there somewhere I can go to learn more details about how knock sensors
work? It sounds like they use a resonant sensor, chosen & tuned for the
application, and maybe look for a build-up of oscillation?

I had this idea to use something like a (non-resonant) quartz transducer,
maybe one per cylinder, to get a signal when each cylinder fires. Then I
could monitor the signal under normal conditions, to get a baseline. A
knock should give a stronger, shorter signal, a bit earlier, right? Even if
it needed a DSP, and tuning for each engine, it'd still be useful to me.

I had heard that some aftermarket ignition system had this kind of setup,
but I can't find any info on any such thing. 

   TIA,
   Chris Conlon

p.s. Hi, I'm new :)