knock sensor

[Roger Heflin]

On Mon, 10 May 1999, Brian Lewis wrote:

> Hello Everyone,
> 
> I am thinking of adding a knock detection circuit to an engine management
> system that I am developing.  What type of signal conditioning do I need to
> add a GM style sensor? What type of output does this sensor produce and how
> do I determine if detonation has occured? Are there any resources on this
> somewhere? Thanks in advance.
> 
> Brian Lewis
> 

I believe the GM sensor is basically a pizeo (sp?) microphone.   There
is a circuit in the ECM (it is a removable chip/module on 94+ vehicles
or is in the chip carrier on pre-94 vehicle (f-bodies, unknown about
other models)).   I believe the circuit in the ECM is some sort of
filter, it is my belief that a better knock sensor could be made with
a more exoitic detection algorithm (DSP).   It is also my belief that
other stuff could be detected with this more exoitic setup (misfires?
listen for the iginition and yell if it is not there).   I believe the
GM filter is a notch filter, and if the energy in the band gets above
a certain amount it sends an output high which signals knock.   The
knock module in the block is a mic though.  All of the "interesting"
knock circuitry is in the ECM as a removable module or in the chip
carrier in the ECM.

			Roger