Spark plug pic's

[Stephen Webb]

> Not all detonation, is audible.  You can run trace, and tip in detonation,
> and never know it.  Do you know what detonation detection strategy Toyo
> uses?.

Not sure.  I have a question that I have been trying to research,
however.  Maybe some people can point me to a good resource.

The basic topic is electronic circuits for knock detection, in particular
using the Bosch style knock sensor.

My project is an '89 VW Cabriolet + a turbocharger.  It's CIS injection,
not EFI, so I've been somewhat reluctant to bring it up.  My focus right
now is on the ignition system, which I suppose isn't strictly EFI, but I
believe is still "on topic" for the list.  I want to build an ignition
control circuit for the vehicle.  It was not originally equipped with a
knock sensor, but I would like to add one.  

I would like to build a circuit that does the following:
1. Ignition timing map based on MAP and engine RPM.
2. Engine knock detection --> ignition retard.
3. Electronic boost control, RPM based
4. Idle air stabilizer valve control

Some of this has changed somewhat because my PIC programmer can't deal
with some of the higher end PICs (I planned on using built in PWM support
for the IAS valve, and other features made it easy to do multiple things
at once)

For now the three issues are:
1.  Safely/correctly interfacing the micro with the hall sender.  
2.  Safely/correctly interfacing the micro with the [stock] ignition
control module. 
3.  Correctly detecting knock from the knock sensor.


I've read the Blue Bosch FI book, and it mentioned engine knock producing
some frequency.  I believe the Bosch Motronic book said that it was
typically in the 5kHz range.  One paper I read said that it varied from
4-8kHz depending largely on engine bore diameter, and a TI whitepaper
(making a case for their cool DSP chips) said that simple frequency
detection wasn't good enough for early and robust knock detection, and
that their DSP solution was the way to go.  I have built a knock sensor
circuit very similar to this one:
http://www.gnttype.org/techarea/projects/knock/circuit.gif
(I believe the one I built is revised;  I can't find the reference right
now)

I was able to get the circuit to beep, but it's hard to convince myself
that it is actually working, properly set up for *my* car, etc.

So, I'd like to learn more about engine knock, and in particular detecting
it with a "Bosch style" knock sensor. 

Thanks

-Steve

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