how does a knock sensor work?

[Mark Agnello]

David,

> 
> Just say it has an extremely high output impedance. 
> That rings my bell, at
> least :)
> 
> That can be solved with a good FET buffer as the
> input stage with a really high
> input impedance around 40 MegOhms.  I reengineered
> the front-end to an AKG 451
> condenser mic once.  The schematic looked something
> like this:

I think many modern automotive knock sensors are
actually designed like this.  They have built in
buffers that hopefully eliminate the sensitivity to
cable condition.

Mark

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