knock knock

[swagaero]

Tom Cloud wrote:
> 
> >for those of you that requested the knock scematic and have not received
> >it yet let me know and I will reship it. Remember computers are not a
> >perfect science (MICROSOFT).
> >       For those of you that did receive it let me know what you think of the
> >simple circuit.
> >
> >Steve "Keep the Greasy side down" Parkman
> >
> 
> I got it .... opened it with MickeyStuff Word and it looks okay;
> prints okay.
> 
>   - have you used this ??  (dumb question, I hope) I built 20 of them and had on all types of engines the only ones that it really was sensitive was lycoming and contintals old tech
> 
>   - have you verified that it works ?? oh yes
> 
>   - the reason I ask is that I'm led to understand that each
>     engine configuration has a very **narrow** band of frequencies
>     that represent knock -- and your .047 uF filter is certainly
>     not "narrow" adjust the window for barly flickering and when it knocks the lights will come on the harder the knock the more lights
> 
>   - this circuit seems to actually just measure "noise", not
>     knock ???? yes Correct every engine is different as you said the worse case is ford.
 .... the input bridge/filter combo is just what
>     is called an "envelope" detector ... i.e. it yields a DC
>     signal proportional to the peak excursion of the input
>     signal and represents the outer "edge" of the signal
> correct 
> I have a long-range plan to take my knock sensor and a spectrum
> analyzer and do some driving (trying to miss running over things
> whilst I watch the spectrum analyzer -- it has no hard copy
> output).  Note that RatShack used to make a hand-held spectrum
> analyzer (or was that a sound level meter ... ???? don't remember
> anymore  8^)
> 
> I guess, Steve, that my first reaction is to question the efficacy
> of this circuit for a cheap circuit it works good the more you spend the better it gets. (bean counters delight)
> 
> Tom Cloud
> 
>        All generalizations are false (there are NO absolutes)


Steve