[Diy_efi] About MAP sensing and it's jitter

[steve ravet]

Alexei Pavlov wrote:
> 
> alexis.pavlov at st.com wrote:
> >
> > tsokorai at xperts.cl wrote:
> > >
> > > Right now in my test code, one sample is taken for every cylinder, as my
> > > timing marks on the crankshaft are 4, 90 deg. apart. That makes 8 signals
> > > every engine cycle (2 crankshaft rotations). Is it a good idea to still
> > > lowpass filter them?
> 
> I've looked at the signal charts. I still find signal dirty.
> The danger with your approach of sampling is to undersample, even
> if many diy EFI systems seem to do the same way.

There's an article on the gmecm page about how GM implements lag filters
for O2, MAP, etc.  It's always a good idea to filter based on your
sample rate.  In the case of MAP you can do it with a small orifice
restriction in the line to the MAP sensor, or electrically, or in
software.

--steve


-- 
Steve Ravet
steve.ravet at arm.com
ARM,Inc.
www.arm.com
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