You made your ECU so you know where you are in the combustion cycle - or=20
you can monitor the spark,
so take your accelerometer samples mid stroke or wherever the least=20
noise is in the stroke.

Also if your engine is a single cylinder 2 stroke or a 4 stroke twin at=20
10 000 rpm,
a processor running at 40 mips has 240 000 instructions per firing of=20
the spark,
you will lose time (instruction cycles) because the power stroke has a=20
duration,
maybe you could use that time to update a display or save a data point.

Trevor Hancock
>> what about a second accelerometer, high pass filter, invert the output
>> and apply a proportion of it to the original accelerometer signal like
>> active noise cancelling.  There's a Microchip ap note or reference
>> design about active noise cancelling in a dsPIC
>>
>> or you might not need the second accelerometer, isolate the vibration
>> frequency and apply the inverse...
>>
>> Sounds easy but I bet it's not.
> Yes also because the MPU cannot really use much of its time in FFT filter=
ing
> (the frequency won't be fixed, as it's linked to the RPM of the engine), =
and
> the frequency analysis I have made on the PC showed that it was a very co=
mplex
> source of noise.
>
> Considering that the sensor wasn't going to add much functionality (but i=
t would
> have been cool to have), I think I'll just give up for this battle.
>
>
>> Trevor Hancock
>> --=20
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