Homebrew Knock Sensor For MS1-E

[Xnke]

Yes, I am going to follow on in Phillip Ringwood's steps and build a knocksensor for my MS1-E. Thanks to the Subaru Engine Project, I now have a good knock sensor, and have plenty of connectors to fit it since it uses an EV-1 plug, just like many fuel injectors.

Preliminary testing shows that this sensor will work very well with the conditioning circuit that is shown in the MS-Extra website, and testing with the scope shows that it is going to be very simple to implement.

More as it happens.

[Xnke]

Ok, so running through the math a little, I figure I can peak the output of the knock sensor at the acoustic resonant frequency of the cylinder. For the Subaru the sensor came from:

F(knock)= (900)/[3.14*(0.0497)]

Where F(knock) is the acoustic resonance of the cylinder
900 is a constant
3.14 is Pi, 'cause cylinders is usually round
0.0497 is the bore radius in meters

For the Subaru EJ25, this turns out to be about 5.7Khz.

So, working for my L28, the formula is:

F(knock)= (900)/[3.14*(0.044)]

works out to be about 6.5Khz. That's close enough, the sensor itself is wideband. I can tune the filter to peak at this frequency, and reject all others.

---------- Post added 06-28-2010 at 12:51 AM ----------

Now I'm thinking about active filtering, something bandpass in nature. The megamanual-extra shows this circuit:

http://www.msextra.com/doc/ms1extra/...ck-circuit.jpg

And it can be easily modified, by taking the 10K resistor and the 10nF capacitor and replacing that simple R-C filter with another op-amp, set up as a bandpass filter for the frequency I am interested in, about 6.5Khz.

more on that when i work out the values needed...

[Xnke]

Ok, Now I have a working filter, so I'll kitbash the two schematics together and post them up in a bit.